ZOOLOGY AND BOTANY, MICROSCOPY, ETC. "99 



given by certain glass insulators, but it is also possible to make pre- 

 liminary acceptance tests upon new insulators, and to eliminate all of 

 those which show signs of improper annealing. 



Evatt, Ev. J. — The Cameragraph : a Drawing Apparatus. 



Journ. Anat. and Physiol., iii. (1908) pp. 335-6. 



(4) Photomicrography. 



Cheap non-vibrating Suspension for Microphotography.* — R. <i. 

 Perkins takes a 2-in. plank 14 in. wide and fixes on it in optical align- 

 ment the various parts of the apparatus. It is of course necessary to 

 have some arrangement so that the light and the collecting lens may 

 be adjusted, though to save expense, a median fixed position may be 

 secured with good results for all powers. The bellows should slide in 

 the focal plane, so as to admit of looking in the eyepiece of the Micro- 

 scope for the area to be photographed. Two cleats of hard wood were 

 screwed to the bottom of the plank near the ends, and through these 

 four screw-eyes were bolted. Four pulleys were fastened on the ceiling 

 with window cord passing from the cleats on the wall through the 

 pulleys and down to the screw-eyes in the plank. At any point between 

 the ceiling pulleys and the screw-eyes, were interposed extension springs 

 of such a tension that the rings would be separated about an eighth of 

 an inch when the whole weight of the apparatus came upon them. The 

 plank and its fixtures were then raised by its cords to a convenient 

 height, the light connected with its source, and the machine was 

 complete. The advantages which have been found in this arrangement 

 are, in the first place, the absolute removal of building vibration, 

 exposures of one second or one hour being equally clear, even with the 

 whole affair swinging to and fro and up and down. In the second 

 place, there are no legs underneath to be kicked or to get in the way, 

 and the plank can be pulled up to the ceiling if desired to give more 

 space in the dark room. In the third place, the plank and the 

 suspension cost only three dollars, besides the time necessary for instal- 

 lation. 



Resolving Power of Photographic Plates.f— G. B. Kenneth Mees 

 points out that, while great attention has been paid to the resolving 

 power of lenses, very little has been done for the resolving power of the 

 photographic plates which are largely used in recording instruments. 

 He considers that the resolving power may be defined as the distance 

 which must separate two lines of light falling npon the plate in order 

 that the developed image may be recognised to be that of two separate 

 lines. It is clearly of no use to obtain a higher resolving power in an 

 instrument than the plate used in that instrument will possess. The 

 only attempt to state this resolving power appears to be that of 

 Wadsworth,$ who lays down that two lines can be separated if between 

 the particles in the maxima of the lines there are one silver particle and 

 two spaces, that is to say, the linear distance between the two maxima 

 or centres of the line is equal to four times the diameter of a particle. 



* Johns Hopkins Hosp. Bull., xx. (1909) p. 325. 



t Proc. Roy. Soc, lxxxiii. (1909) pp. 810-18 (8 figs.). 



\ Astrophys. Journ., iii. (1896) pp. 188, 321. 



u 2 



