Page:Popular Science Monthly Volume 13.djvu/460

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444
THE POPULAR SCIENCE MONTHLY.

The cliché is now left to dry for twenty-four hours, and it is trimmed all around. Then, at one corner, the paper is separated by a finger-nail from the coating formed upon it. Having in this way loosened the coating at one corner, it may easily be stripped off altogether, with a little care, leaving the paper clean and white, as though it had never undergone any treatment. In this way is got a negative at least as transparent as though it were on glass; but it possesses the advantages of not being brittle, of not being damaged by rubbing, of occupying but little space, and, finally, of giving better proofs than can be got from clichés on glass.

To utilize this process, M. Deyrolle has constructed a strong but portable apparatus, made almost entirely of copper and iron, weighing not over 400 grammes for one producing proofs 0.13 metre by 0.18 metre, or 700 grammes for one producing proofs 0.24 metre by 0.18 metre (see figure on page 443).

The camera, which, when folded, is only four centimetres high, is held distended by two steel rods, which connect the frame of the object-glass with that for the slide. The support for the apparatus consists of three double legs with joints; these are fastened by thumb-screws to a triangular table. The stem supporting the camera is articulated with the centre of this table by means of a ball-and-socket joint, which allows the instrument to be turned in any required direction. The ball may be made fast at will by means of a steel spring. This new form of foot has the great advantage of being extremely light, and of allowing the camera to rest in any plane whatever.

We would add that, when this system is employed, the complete outfit of an explorer who wishes to take 300 negatives will not weigh over six kilogrammes, including the instrument, the clichés, and all the chemicals needed for developing the negatives.

 

VOLUNTARY MOTION.
By Professor PAYTON SPENCE, M. D.
"The primitive elements of the will have been stated to be—1. The spontaneity of movement; and, 2. The link between action and feeling, grounded on self-conservation. In the maturing or growth of the will, there is an extensive series of acquisitions, under the law of retentiveness or contiguity" (Bain, "Mental Science," p. 318).

"The elements of voluntary power being assumed as—1. Spontaneity; and, 2. Self-conservation, we have to exemplify the connection of these into the matured will, by a process of education" (Bain, "Mental Science," p. 325).

TO what extent we differ from the above propositions, and especially from those parts of them which we have italicized, will more fully appear in the following article.