Imágenes de páginas
PDF
EPUB

itself multiplied by the distance of the luminous point from the aperture added to the distance of the aperture from the screen, and divided by the distance of the luminous point from the aperture. Hence it is obvious that the size increases more slowly than the distance of the screen from the aperture, and in the case of a distant object, like the sun, almost imperceptibly. When neither the aperture nor the luminous object is a physical point, each strives to imprint its own figure upon the screen, and the resulting shape will resemble that of the aperture or the object according to the size of the two images which each would separately impress, as calculated above. If the size of the aperture is to the size of the luminous object as the distance between the aperture and screen is to the distance between the luminous body and the screen, the separate images which the aperture and the luminous body will form are of the same size, and therefore their shape is equally influential in forming the resulting fig. ure. When the distance of the screen is thirty feet from the aperture, the two images above described are of the same size with solar light if the aperture is between three and four inches. Now when the distance between the screen and the aperture is changed, the size of the image which belongs to the luminous body changes much more than that which belongs to the aperture. Consequently, if the screen on which the images are painted is much farther than thirty feet, the size of the aperture being three or four inches, or if the size of the aperture is diminished, the distance between the screen and the aperture remaining the same, the influence of the sun's form will prevail, and in extreme cases the resulting figure will represent the shape of the sun to the exclusion of all trace of the shape of the aperture. Hence with very small apertures the final image will have no resemblance in shape to the aperture, except when received very near to the aperture. But with nearer bodies, as the flame of a candle, the shape of the aperture continues upon the screen at larger distances, or with the same distance when smaller apertures are employed.”

Four hundred and fourth meeting. September 12, 1854. — Monthly Meeting. The PRESIDENT in the chair.

The Corresponding Secretary read letters from Sir William Hamilton, accepting his appointment of Foreign Honorary

VOL. III.

21

[graphic]

Member; and from Dr. Walter Channing, resigning the Fellowship of the Academy.

Dr. Hayes presented a pamphlet, “ Reminiscences of GlassMaking,” by Deming Jarves, accompanying the donation by some remarks on that art. He stated that at the present time the United States are before all other countries in the manufacture of flint glass, both in the quality and quantity of the article produced.

Dr. Hayes also presented the report of the committee of the Franklin Institute, with one of his own appended, on E. G. Pomeroy's new process of coating iron with copper, and exhibited iron spikes coated by the process described.

Professor Lovering exhibited to the Academy Plateau's new instrument, the Anorthoscope, and explained its construction and use.

Professor J. Wyman said, that since the previous meeting, in consequence of the remarks then made on the form of the image produced by the sunlight in passing through apertures of various shapes and sizes, he had examined the pupil of the eye in various animals with reference to the point in question. Professor Wyman described this as it exists, of various shapes; but he found by experimenting with apertures of similar shapes cut in cards, that the image of the sun transmitted through them remained always the same, with the exception of a greater or less penumbra at the circumference.

Dr. C. T. Jackson gave an account of the recent discovery of gold at Bridgewater, Vt., where it is found in a vein of quartz a foot and a half thick, in company with sulphuret of lead, silver and copper pyrites. One ton of reduced lead from this locality yields over six hundred dollars' worth of

gold.

Four hundred and Afth meeting.

October 10, 1854. — Monthly Meeting. The CORRESPONDING SECRETARY in the chair.

Professor Agassiz called the attention of the Academy to the recent decease of one of the Fellows, Dr. Waldo I. Burnett, and made the following remarks : —

" I rise to perform a sad duty, which, but for my absence, I would have performed sooner. The American Academy of Arts and Sciences has sustained a severe loss by the death of its associate, Dr. W. I. Burnett, who, after a protracted illness, expired of consumption. Dr. Burnett had hardly yet entered upon the stage of active life when disease began to shake his constitution; but such was his devotion to science, such his zeal and perseverance, that, in a state of health which would have prostrated most men, he was unceasingly active and industrious. The consciousness of the probably short duration of his life, of which he spoke occasionally, and always with the greatest calmness, seems to have been a powerful stimulus for him to leave nothing within his reach undone which might advance the cause of science, and secure for himself an honorable place among its devotees. In this respect his short life has been most exemplary. He not only made his way by himself, but he devoted every moment of his time to the increase of his knowledge, rather than to the improvement of his worldly condition. His efforts were crowned with the fullest success, and the papers he has communicated to the Academy, one of which is already published in its Memoirs, and his other scientific contributions, will ever bear testimony to his industry and skill. He was one of the few among us extensively conversant with the whole range of foreign publications upon the subjects with which he was engaged. In his intercourse with his fellow-laborers in the field of science he was modest, unpretending, and ever willing to aid others. As a friend he was true and open. All these amiable and distin. guished qualities make his departure from among us a real loss to all true lovers of science. I therefore move that the Academy pass the following resolutions, as expressive of its sense of his great moral worth and scientific eminence.

Resolved, That the Academy feels deeply the loss of its distinguished associate, Dr. W. I. Burnett, who, by his untiring industry, his great scientific accomplishments, and his amiable personal qualities, stood prominent among the rising generation of scientific men in America.

Resolved, That the Academy will cheerfully undertake to print in its Memoirs whatsoever papers he may have left in a condition fit for publication.

Resolved, That the American Academy tenders, to the family of Dr. Burnett its sincere sympathies for their irreparable loss.

Resolved, That a copy of these resolutions be sent to the family of Dr. Burnett, and printed in the public papers."

These resolutions were seconded by Dr. S. L. Abbot, and unanimously adopted.

Professor J. Lovering then rose, and said :

“ May I call the attention of the Academy to another loss it has sustained in the recent and sudden death of Macedoine Melloni, the news of which arrived in this country almost contemporaneously with the report of a new paper which he had presented to the French Academy. In the preface to his great work, La Thermochróse, Mel. loni confesses the great admiration which he had felt for nature from his youth : « Mais rien ne frappait autant mon imagination que le lieu si intime qui reunit les phénomènes de la vie à l'astre brillant du jour.' He began to teach Physics as soon as he left the school-bench, and continued at that employment for seven years, from 1824 to 1831, when the courses of the University of Parma were discontinued. Here he came into valuable contact with Nobili, whose thermo-multiplier he adopted and perfected with the assistance of the skilful artist of Paris, Ruhmkorff. Political troubles banished Melloni from Italy, but he found an asylum in France, and a kind friend in Arago. He accepted a Professorship in the Department of the Jura, and after. wards went to Geneva for six months. In 1837 Arago prevailed with Metternich to obtain permission for the return of the exile to his home, and in 1839 Melloni was appointed Director of the Cabinet of Arts and Trades at Naples.

“ Melloni's discoveries in Radiant Heat began with his first memoir presented to the French Academy, in 1833. This was followed in long succession by others in French and Italian to the day of his death, or for a period of more than twenty years. The fruits of Melloni's labors were systematically embodied in his great work, entitled La Thermochróse, ou la Coloration Calorifique, the first volume of which

appeared at Naples in 1850, dedicated to Humboldt and Arago. The title of this work suggests one of the most brilliant, as well as earliest discoveries of Melloni, namely, the existence of variety among rays of heat similar to those peculiarities of light which are called color. As heat itself does not address the eye, so its varieties cannot. The color of heat, as the phenomenon is metaphorically called by Melloni, is not perceived by the eye, but shows itself in the same way that the colors of light appear in experiments on absorption and prismatic dispersion. Moreover, the transcalency of a body is often disproportioned to its transparency. To these researches may be added those on the radiation and absorption, the polarization and depolarization and interference of heat, with incidental investigations in regard to the heat of moonlight and the action of the eye; the whole perfecting and almost creating a new branch of physics, for the complete illustration of which Melloni provided in the world-renowned thermo-electric multiplier and other apparatus as arranged by Rubmkorff. In view of these great services to science, which have established the undulatory character of radiant heat, whatever may be the statical condition of this force, and have placed the name of Melloni among the highest in physical science, I propose the following resolutions : —

Resolved, That the American Academy of Arts and Sciences has heard with deep regret of the sudden death of its illustrious Foreign Honorary Member, Macedoine Melloni.

Resolved, That the Academy fully appreciates the high services which Melloni has rendered to the physical sciences by his brilliant discoveries in Thermotics, which he has exalted to an eminent rank among the oldest and best cultivated fields of research ; and that it recognizes in him, not only an early, long, and deep passion for the study of nature, but also remarkable experimental skill, displayed alike in the contrivance and use of new instruments, as well as unusual caution of mind and excellence of style in communicating his discoveries.

Resolved, That the American Academy unites with the other scientific associations throughout the world in deploring the sudden going down of one of its most brilliant lights, while in its meridian splendor.”

These resolutions were seconded by Professor Agassiz, who, together with Professor Gray, offered a tribute to the great

« AnteriorContinuar »