444 THE POPULAR SCIENCE MONTHLY. 



The cliche 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 cliches 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 cliches, 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 sponta- 

 neity of movement ; and, 2. The link between action and feeling, grounded on 

 self-conservation. In the maturing or growth of tbe 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' 1 ' 1 (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. 



