Imágenes de páginas
PDF
EPUB

For the first paper the council of the Royal Society awarded the gold medal as a mark of their appreciation of its practical investigations.

He was appointed professor of the mechanical principles of engineering at University College, London, on the 6th of February, 1847, and lectured during the sessions of 1847 to 1853, inclusive. In 1847 he was appointed a member of the royal commission to inquire into the properties of wrought and cast iron and their application to railway structures. The results of his labors in this important inquiry are given, with marked reference to their magnitude and efficiency, in the commissioners' report of 1849. He was consulted by the late Robert Stephenson in reference to the construction of that great national work, the tubular bridge over the Menai straits. His experience and mathematical knowledge enabled him to suggest and carry out a series of experiments, at the cost of several thousand pounds, with a view to investigate the bearing properties of wrought iron rivited tubes, and to satisfy the mind of this great engineer as to the stability and safety of the Britannia and Conway tubular bridges. He edited an edition of "Tredgold on Cast Iron," to which he added a second volume, giving an account of his own experiments and discoveries, published by Weale, 1846. The title of the second volume is, "Experimental Researches on the Strength and other Properties of Cast Iron, with the development of New Principles, calculations deduced from them, and inquiries applicable to Rigid and Tenacious Bodies generally."

The most novel and important conclusions here given are as follows:

The strengths of long pillars of cast iron, wrought iron, cast steel, and Dantzic oak, of the same dimensions, are in proportion to the numbers 1,000, 1,745, 2,518, 109. Cast iron is not reduced in strength when its temperature is raised to 600°.

The sets, in cast-iron beams, vary nearly as the square of the force of deflection; hence any force, however small, will injure the elasticity of cast iron. The strength in tons of beams approaching the best form is measured by the formula 2.166ad÷1, where a area of section of bottom flange in the middle, d= the depth in inches of the beam, and 7 the distance in feet.

A general investigation of the position of the neutral line is given on the principle that the forces of extension and compression of a particle vary as any function of its distance from the neutral line. This includes every hypothesis which has been proposed in order to compute the strength of material bodies subjected to strains.

BIRTH AND EDUCATION.

As I have already stated, Mr. Hodgkinson was born at Anderton, Cheshire, in the year 1789. His father, a respectable farmer, died of fever when his son Eaton was about six years of age, leaving Mrs. Hodgkinson with two daughters and a son. On his father's decease his mother determined to continue the farm; and by industry, thriftiness, and business-like habits she was enabled to educate her children respectably, and to send her son to the Grammar School of Northwich. At this school he received the rudiments of a classical education, as he studied the Latin, Greek, and Hebrew languages under the immediate supervision of the head master, Mr. Littler. This was done to meet the wish of his uncle, the Rev. Henry Hodgkinson, rector of Aberfield, Berkshire, who was very anxious that his nephew should be educated with a view of going to Oxford or Cambridge, to prepare for the church. The desire of his uncle was, for a time, gratified, and the hope was strongly indulged that one day Eaton Hodgkinson would be a student of one of the universities; hence the study of classics in his early youth was considered indispensable, although it was not exactly in conformity with his tastes and habits of thought, as at an early age he was naturally more inclined to the study of mathematics than of languages.

To the severe treatment which he here suffered, his cousin, Mrs. Thompson, attributes the nervous tremor of his hands and speech which continued with him through life, and was a serious impediment to his success. The Rev. Mr. Littler was a very severe disciplinarian, and if a boy could not learn he tried to flog it into him; and young Hodgkinson, owing to his inaptitude for languages, having received a sound thrashing for not having learned his lessons perfectly, was removed from the grammar school and placed in a private school in Northwich of far less pretensions, but more in unison with his aspirations.

This private school, to which he was removed because he did not show a decided taste for the study of languages, was conducted by Mr. Shaw, a gentleman of superior mathematical attainments, and possessing great tact in teaching and in the general management of boys. It was at this school that Mr. Hodgkinson finished his youthful education. He obtained a good degree among his school-fellows, and a distinguished position in the affections of his master. The instructions of Mr. Shaw in mathematical subjects were fully appreciated by Hodgkinson, and consequently he made rapid advances in the various studies to which his attention was directed. Here he laid the foundation of that mathematical knowledge which he afterwards applied with singular success to the extension and development of the theory and practice of the strength of materials. The bias of Mr. Hodgkinson's mind at this period, and the position in which his mother was left, seemed to require a reconsideration of his future. He was now growing in stature as well as in knowledge, and his mother found him very useful to her in the outdoor work on the farm; therefore it was deemed desirable to abandon the idea, once strongly entertained, of prosecuting her son's education with a view of entering the church, and to allow him to devote his attention and energies to the skilful management of farming.

Mr. Hodgkinson therefore gave up all thoughts of the church, and Latin, Greek, and Hebrew were changed for more congenial subjects of study. He commenced at once his career as a Cheshire farmer; but although he felt it a duty to assist his dear mother, and meet her wishes to the best of his ability, still he made but little progress in his new vocation. Farming, which had been thrust upon him by sheer necessity, was not suited to his genius; but he pursued it for a time as a paramount duty, from which his conscientious devotedness to his mother and sisters would not allow him to escape. The seeds of pure and mixed science, which had been thrown broadcast into his youthful mind by Mr. Shaw, were now beginning to germinate, and to rise from their latent state into full and sensible existence, creating, as they advanced to maturity, new wants and fresh desires, which could not be gratified by farming or the society of a Cheshire village. The fruit thus developed at the village school indicated, with unerring certainty, a different direction from Cheshire farming or the church. His mother saw this, and she was ready to bend to circumstances which she could not successfully resist. Hence he persuaded her to give up her farm in Cheshire, and embark her small capital in a pawnbroking business at Salford, Manchester. Their friends advised this step, as the best to promote the interests of the family and satisfy the thirst of Mr. Hodgkinson for scientific knowledge and society. The family, therefore, moved from Great Budworth, Cheshire, to Salford, Manchester, in the year 1811, when Mr. Hodgkinson was about 22 years of age. This step was the turning-point of his career, and but for this in all probability he would have past a life of inglorious ease in a Cheshire village, unknown as a cultivator of mathematical and physical science.

His residence in Manchester was soon productive of important consequences; his habits of thought became fixed, and the line of scientific inquiry in which he was to advance was not long left indeterminate. Manchester at this period was in its youthful vigor; it contained men of great intellectual endowments, each anxious to distinguish himself in some department of useful knowledge; among these the names of Dalton, Henry, and several others stand out pre-eminent.

The business, under the control and management of Mrs. Hodgkinson, assisted by her son and daughter, was successful.

Mr. Hodgkinson's spare moments from business were now entirely devoted to reading any standard works on science which he could procure. The works of Simpson, Emerson, and Dealtry contributed greatly to his knowledge. He read these authors with earnestness and fidelity, and was wholly indebted to them for his knowledge of the higher departments of mathematical research. Many of the self-taught men of the last and the beginning of the present century have expressed their obligations to Thomas Simpson and William Emerson. Their works, whatever prejudice may think or say to the contrary, were the best standard works of the age; and it may be affirmed that the scientific literature of the eighteenth century is accurately and faithfully reflected from the pages of the weaver of Market Bosworth, Thomas Simpson, and the Hurworth village schoolmaster, William Emerson. These humble but highly gifted men were more catholic in their writings than are the authors of the present age. They wrote to instruct the mass of mankind, but the writers in these days labor for a special purpose, which is limited in its operation: they write only to supply the daily routine of the school, without casting a single thought beyond its boundary. The late Rev. Robert Murphy, a Cambridge mathematician of distinguished eminence, speaks of Thomas Simpson as an analysist of first-rate genius. (See "Murphy's Equations.") M. Clairaut, when in England, paid Simpson a visit at Woolwich, in order to compare his own investigations on the motion of the moon's apogee with the investigations of Simpson on the same subject. This fact alone shows the high position in which Simpson stood in the estimation of the most eminent mathematicians of Europe.

In consequence of his ardent love for scientific pursuits, Mr. Hodgkinson became acquainted with the most gifted men then living in Manchester. Dr Dalton, Holme, Henry, Ewart, Sibson, Johns, Fairbairn, were among the scientific friends with whom he could freely converse on subjects which possessed a mutual interest. In his mathematical reading he sought and obtained the help of Dr. Dalton, who was then a private teacher of mathematics in Manchester. He became one of Dalton's pupils, and read with him the works of Lagrange, Laplace, Euler, and Bernoulli, whose writings were now engaging the attention of the best and foremost mathematicians of England. These authors had been instrumental in producing a great change in the mathematical sciences at Cambridge; their investigations were models of elegant algebraical demonstration, both with regard to symmetry of notation and subject-matter of inquiry. The friendship of Dalton and Hodgkinson, cemented by genial minds and kindred pursuits, continued uninterruptedly till the death of Dalton. Though each of these men had his distinctive field of labor, yet each could hold converse with the other on their respective researches, and Mr. Hodgkinson entertained through life a profound respect for the high character and great chemical discoveries of his friend. The extent of his mathematical reading at this period may be estimated by referring to his paper entitled "On the Transverse Strain and Strength of Materials," printed in the fourth volume of this society's memoirs.

HIS CHARACTER.

The late Professor Hodgkinson, like a true philosopher, was satisfied with a small but adequate competency, and, retiring from business at an early period, he devoted a long life and rare mental gifts to the development of science. And it is a pleasing reflection that while many men very eminent in the history of science have had to wait a long time before their discoveries have been recognized and adopted, Mr. Hodgkinson had the unusual pleasure of seeing the fruits of his labors appreciated and applied to the construction of great practical engineering enterprises. The youthful days of Mr. Hodgkinson were not

marked by precocious talents and wonderful achievements; still he possessed, even in youth, a quick perception of the relations of abstract magnitudes, and manifested, like Newton and Stephenson, a strong propensity for making sundials.

Manhood developed in him a profound intellect, a highly cultivated intelligence, unwearied perseverance, and a kind and an affectionate heart. He discharged every relation of life with fidelity, and has left behind him a name great in the annals of science, reflecting every manly virtue, and unsullied by any act of meanness. He was, however, very jealous of the products of his own mental labors, which he regarded as personal property, and was also equally just in the use of the mental property of other cultivators of science, as he would not appropriate the conclusions of any man without due acknowledgment If he did entertain any hostile feeling, it was against those who, as he conceived, were unscrupulous in their appropriation of the fruit of other men's brains. His sense of justice would not allow him to show the slightest sympathy with this class of offenders.

The efficiency of Mr. Hodgkinson's lectures at University College, and of his oral instruction generally, was somewhat circumscribed by his hesitancy of speech. This peculiarity interfered with his usefulness as a speaker and teacher, and rendered his explanations of subjects, even those with which he was most familiar, somewhat tedious to the student. And it is perhaps one of the greatest evidences that can be recorded of the power of his mind, that he was thought worthy, in spite of his embarrassed address and slowness of speech, to be installed in a professorial chair in one of the leading scientific colleges of the kingdom. As a relaxation from severe mental toil, he cultivated a taste for general literature and the architecture of the middle ages. Of late years he frequently travelled, both on the continent and in the British empire, to examine those stupendous cathedrals and other public buildings which adorn western Europe, and which testify to the good taste, piety, and intellectual culture of the age in which they were built. He was fond also of investigating the remains of antiquity. And, what is valued above all by a man of science, he enjoyed the friendship and esteem of his contemporaries, who were able to estimate his worth, appreciate his talents, and apply his discoveries to useful purposes. The most eminent engineers of the age placed unbounded confidence in the results of his experiments, believing them to be faithfully recorded and accurately reduced to meet the requirements of mathematical formulæ. As a confirmation of this, it may be stated that the engineers' pocket and text-books of the present time are full of Hodgkinson's formulæ for calculating the strength and deflection of pillars and

beams.

Mr. Hodgkinson was twice married, but without issue in each case. His first wife was Miss Catherine Johns, daughter of the respected Rev. William Johns, a distinguished member of this society, who contributed an interesting paper to its memoirs, entitled "Remarks on the Use and Origin of Figurative Language," (vol. ii, new series.) His second wife was Miss Holditch, daughter of Henry Holditch, esq., captain in the Cheshire militia. This lady, who is now left to mourn her loss, devoted her powers to comfort and sustain her husband when his health and memory would not admit of his having recourse to his favorite pursuits. Of late his great mental powers became prostrate, and his memory failed so much that it was obvious to his friends the time had arrived when his faculties required repose. In this state of mental lassitude the services of Mrs. Hodgkinson were of great value to him. It is not unusual with men whose mental powers have been overstrained by excitement and hard labor that the desire for intellectual activity does not cease when the physical power necessary to sustain it is feeble. Mr. Hodgkinson was the subject of this painful' experience the desire for mental activity continued unabated to the last; and it was only a few months before his decease that he was engaged in arranging

his papers, with a view to publish them, so that they might be more accessible to engineers than they now are in the volumes of learned societies.

Mr. Hodgkinson's religious emotions were silent, devotional in the highest sense-not sectarian; they were strictly confined to the channel between his Maker and his own soul. And in this way they were purified by the truth from heaven, bearing the precious fruit of meekness, charity, and implicit confidence in Him who is all and sustains all. His religion was the arbiter of his life, the judge of the many and important obligations between God, his fellow-man, and himself. His end was peaceful, and he has left a name marked by strict integrity, which will be well remembered in the walks of science for ages yet to

come.

Let us now pass on to notice more in detail the works of Mr. Hodgkinson, which have raised him to a good degree among his contemporaries, and will also be the introduction to future thinkers in the same field of labor which he successfully cultivated.

"On the Transverse Strain and Strength of Metals," (read March 22, 1822.) The objects aimed at in this paper are, as stated by the author, to unite, in a general formula, the commonly received theories in which all the fibres are conceived to be in a state of tension; and next, to adapt the investigation to the more general case, where part of the fibres are extended and part compressed, and to seek experimentally for the laws that regulate both the extensions and compressions. The manner in which these objects have been sought and developed is a model worthy of every commendation, of clear, sound, geometrical reasoning and refined artifice. And the data necessary to give practical effect to the various analytical formulæ have been obtained from experiments, than which none have been recorded with greater fidelity and less contortion to meet the demands of particular theories. No painstaking or expense was considered too great to make the results of the experiments successful and trustworthy, so that the engineer and philosopher alike could place implicit reliance upon them. In these experiments there is recorded, for the first time, an element which has furnished a theme for many animated discussions of late years among philosophers and practical engineers, and which became an important object of research in all Mr. Hodgkinson's subsequent experiments, viz., set, or the difference between the original position of a strained body and the position which it assumes when the strain is removed.

This point, which is full of interest and important consequences to the practical man, cannot now be discussed. On examination I believe that I shall be borne out in the statement that, notwithstanding the number of books which have been written during the last 30 years on the strength and strain of materials, some of a more ambitious kind, and others having the humbler object of being useful in communicating information to the artisan, still there is none from which、 a clearer and more satisfactory exposition of this subject can be gathered than from the paper above referred to by Mr. Hodgkinson, in the volume for 1822. The Tuscan philosopher, Galileo, has the merit of first propounding a theory of the strength of materials, and applying the unerring principles of geometry to the computation of the strength of beams of given dimensions. With Leibnitz originated the idea of the force of extension of a fibre being proportional to its distance from the lower side of a bent beam. James Bernoulli first suggested the notion (for it never assumed any other shape in his mind) of a neutral line in the section of rupture. But to the late Professor Hodgkinson belonged the merit of giving practical effect, in this paper, to the happy suggestion of Bernoulli, by showing, both theoretically and experimentally, the true method of determining, in the section of fracture, the exact position of the neutral line, and of calculating the strength of the beam.

In order, then, to show more clearly the steps taken by Mr. Hodgkinson in

« AnteriorContinuar »