268 THE AMERICAN MONTHLY [Sep 



edge that can be reached only through the microscope, 

 the day may perhaps be not so far distant when the mi- 

 croscope, as an aid to nature study, will be used more ex- 

 tensively and more seriously in our public schools than 

 it is at present. There is no reason whatever why a com- 

 pound microscope of low magnifying power should not be 

 just as much as a common appurtenance of a well-regu- 

 lated elementary school as a blackboard or a piano. 



Book. — All who are interested in microscopy and pho- 

 to-micrography should obtain a copy of an interesting 

 little brochure entitled "Orthochromatic Photography," 

 which is being distributed gratis by Messrs. Cadett and 

 Neall, Ashstead, Surrey. 



Light Filter. — We have recently had an opportunity 

 of experimenting with the "Absolutus" light filter used 

 in conjunction with the Cadett Lightning Spectrum plates. 

 The great rapidity of these plates, the sensitometer num- 

 ber of which was 360, renders them especially suitable for 

 photographing the movements of microscopic plants and 

 animals, while their extreme sensitiveness to all color 

 luminosities of the spectrum, excepting a very small mar- 

 gin at the extreme red end of the spectrum, enable them 

 to represent with great delicacy the gradations in the 

 colored luminosities of stained preparation*. The ''Ab- 

 solutus" light filter, which is specially adjusted for the 

 spectrum plate, renders all gradations correctly with but 

 a very small margin of error. It may be used either be- 

 fore or behind the objective. Its use increases the expo- 

 sure at a window with a northern outlook about twenty 

 times, but this is really no drawback with the Lightning 

 plate, as, owing to its great rapidity, the exposure neces- 

 sary is invariably shorter than it would be when using an 

 ordinary plate without a filter. The surfaces of the "Ab- 

 solutus" are optically worked, and the coloring accurate- 

 ly adjusted by the help of Abney's color sensitometer to 

 suit the spectrum plate. Workers with light filters know 



