24 CAMERA LUCIDA. 



it being expressly understood that no light shall escape toward the 

 observer, except that which first reaches the object. A Beck lamp 

 is conveniently adapted to this purpose. If a piece of drawing- 

 paper is placed beneath the ocular, and the room darkened, a 

 brilliant image will be projected on the paper, and its reproduc- 

 tion can be easily accomplished with a maximum of rapidity 

 and a minimum of discomfort. In guiding the pencil the 

 draughtsman uses both eyes, and his spectacles if needed, and 

 sits in whatever position he finds most comfortable. 



The general disposition and arrangement of the apparatus will 

 be readily understood by an examination of the accompanying 

 cut (Fig. 5). 



With a proper lamp, and careful utilisation of its light, this 

 device gives excellent results with amplifications up to four and 

 five hundred diameters. 



If a sensitive photographic plate be substituted for the drawing- 

 paper, an exposure of a few seconds will impress an image that 

 may be developed in the usual way. — New York Medical Journal. 



Mosquitoes are said in the Quarterly Review to have been 

 frozen on to the surface of a lake in the evening, and thawed 

 again by the morning sun into animation. Alpine climbers some- 

 times pick up butterflies lying frozen and brittle on the snow, 

 which revive and fly away when taken to lower warmer regions. 

 Insects which habitually hibernate, as larvae and pupae, do not 

 suffer from being frozen for a lengthened time ; but they suffer in 

 open winters from frequent alternations of wet, warmth, and cold. 



The Asteroids.— According to calculations by M. L. Niesten, 

 all the asteroids known (now more than 300), if combined into one, 

 would form a body not quite 514 miles in diameter, or less than 

 one-twentieth the diameter of the earth ; and it would require 

 S>575 bodies like it to form a planet having the volume of the 

 earth. The largest of the asteroids, Vesta is 230 miles in diameter, 

 and the smallest Agatha, four and-a-half miles. As all these bodies 

 having considerable size have most probably been discovered, 

 the estimate of the mass of the whole is not likely to be materially 

 affected by the detection of new ones. 



