the conducting effect of wires may be represented by a logarithmic curve. Among electrical memoirs there is one on the tidal motions exhibited by liquid conductors, and one on the electro-motive power of heat, explaining the construction of some new and improved forms of thermo-electric batteries. An abstract of these improvements is given in the last edition of the 'Encyclopædia Britannica' (Art. Voltaic Electricity).

"Dr. Draper was the first person to obtain photographs of the diffraction spectrum given by a grating, and to show the singular advantages which that spectrum possesses over the prismatic investigations on radiations. In a memoir on the production of light by chemical action (1848), he gave the spectrum analyses of many different flames, and devised the arrangement of charts of their fixed lines in the manner now universally adopted. A memoir on phosphorescence contains the experimental determination of many important facts in relation to that property. Among purely chemical topics he has furnished a method for the qualitative determination of urea by nitrous acid."

[From 1860 to 1870 Dr. Draper did but little in scientific research, devoting himself mostly to historical works. During this time he published his "History of the American Civil War," in three volumes.]

"In the summer of 1870, Dr. Draper suffered a severe bereavement in the loss of his wife. Of Brazilian birth, she was connected with an ancient and noble Portuguese family. She had rendered his domestic life

77 a course of unbroken happiness, and doubtless she was the examplar before his eyes when he wrote that oft-quoted passage in his 'Physiology,' in which, after depicting the physical and intellectual peculiarities of woman, he says: 'But it is in the family and social relations that her beautiful qualities shine forth. At the close of a long life, checkered with pleasures and misfortunes, how often does the aged man with emotion confess that, though all the ephemeral acquaintances and attachments of his career have ended in disappointment and alienation, the wife of his youth is still his friend? In a world from which everything else seems to be passing away, her affection alone is unchanged; true to him in sickness as in health, in adversity as in prosperity, true to the hour of death.'"

Of their six children, one died in infancy; the survivors are three sons and two daughters. Of the former, the eldest, Dr. Henry Draper, Professor of Natural History in the College of the City of New York, is eminent as a physicist and astronomer; the second, Dr. John C. Draper, is Professor of Physiology in the University of New York; the third, Dr. Daniel Draper, is Director of the Meteorological Observatory in the New York Central Park, where he has exercised an important influence in developing the meteorological system of the United States. In recent years, Dr. Draper published two short memoirs: one on the "Distribution of Heat in the Spectrum," showing that the predominance of heat in the less refrangible

regions is due to the action of the prism, and would not be observed in a normal spectrum, such as is formed by a grating; and that all the rays of light have intrinsically equal heating power; the second an investigation of the distribution of chemical force in the spectrum. The Popular Science Monthly notes to his credit that "these scientific researches, to which so many years of his life have been devoted, have been at his own expense; he has never received any extraneous aid, though many of them have been very costly; he has never taken out any patent, but has given the fruits of his investigations and inventions freely to the public.”

ILLUSIONS.

BY THOS. FOSTER.

THE senses are the means by which, directly or indirectly, all observations are made, and science can only make real advance in so far as it is based on observation and experiment. It is most important, therefore, that either our senses should be trustworthy in their action, that is, should give us true information, or (if they neither are absolutely trustworthy originally, nor can be so trained as to become so) that we should be able to test and to correct their indications.

Now it very soon appears, when we put the matter

to the test, that the direct evidence of the senses is not to be accepted without careful cross-examination. The science of our day may be regarded as having been established in opposition to the apparently obvious evidence of the senses. Take, for instance, astronomy. Nearly everything that the eyes tell us about the heavenly bodies, and nearly all that the sight and touch tell us about the earth (so far as astronomy has to deal with the earth as one of the planets) is false. Not one of all the stars we see in the skies is really where we see it. The earth seems flat, large, and fixed; it is really a globe, small compared with the seemingly small stars, and it is moving in many ways, not one of which the senses correctly appreciate. It is the same with other sciences.

We are not concerned, however, to discuss here how far the apparent teaching of the senses has to be analysed before its real meaning can be understood. The examples illustrating this would cover the whole range of science. For instance, to show how the real place of a star can be determined-more or less exactly—from its apparent place in the sky, we require to discuss the laws of refraction, aberration, the proper motion of stars, and a number of other matters. In such cases as this, though what the eye tells us is in a sense incorrect, the eye is supposed to do its work correctly. The eye tells us truly that the rays received from the star by it have come in such and such a direction, and what science has really to do is to determine in what direction those rays must have

set out, in order, after various changes of direction due to the various media through which they passed, to reach the eye, situate on a moving and rotating body like the earth, in the direction which they hador at least seemed to have-or, more strictly, in order to produce an image of the star on such and such precise part of the retina.

But there are many cases in which the senses seem actually to convey false information, the eye telling us wrongly about the shape, size, position, &c., of an object, the touch deceiving us as to its form and qualities, the hearing, the smell, the taste, each in its own way deceiving us. It is such cases as these that I propose to examine. It is most important for the student of science that he should be aware of the various forms of error into which the direct action of the senses may lead him. I could cite instances where, for want of precisely such information, the student of science has been at the pains to explain a phenomenon which had no real existence, or which was precisely the reverse of the truth. Mr. Proctor mentions somewhere a case where a French astronomer (Chacornac) was careful to explain why the edge of Jupiter's disc is brighter than the middle, the fact being that the middle is brighter than the edge, the apparent brightness of the edge being a mere delusion. It may be added that the discussion of the class of illusions referred to is full of interest. The reader will find that the careful consideration of the cause of illusions will generally suggest other illusory experiments,