1898.J MICEOSCOPICAL JOUKNAL. 195 



some tests already made I think I am safe in saying that 

 owing to this device I shall be able to photograph with 

 less than the one-tenthousandth part the intensity of light 

 formerly considered necessary. This improvement is 

 applicable to photography in general, but especially so 

 to photomicrography. First by using the wider lenses 

 of the double microscope, I photographed with the 

 1-1, 300th the usual amount of light, thus making a mag- 

 nification of 360,000 diameters or 129,000,000,000 times 

 the area possible. Exclusion of dust particles promises 

 to permit the use of a hundreth part of this latter 

 amount of light, that is, it makes possible the photo- 

 graphy of over three amd a half million diajneters or 



*over 12,000,000,000,000 times the area. 



But I found another source of trouble in the use of 

 such very faint light, namely, the leakage of actinic rays 

 through the wooden and leather walls of the camera and 

 through the imperfectly-fitting sliding joints and con- 

 nections of the microscopes. With reference to ordinary 

 photomicrography this leakage is but a small percentage 

 of the amount of light which reaches the sensitive plate, 

 but when we get beyond a sixth-inch objective in the 

 first microscope and a sixth-inch in the second, we are 

 dealing with quantities of light much less than the 

 amount of leakage in the best cameras probably ever be- 

 fore constructed. A sixth-inch objective can magnify, 



swith proper oculars and tube-lengths, at least 600 diam- 

 eters, which is an area of 360,000 times that of the ob- 

 ject. Hence any point of the magnified image has only 

 the one-three-hundred-sixty-tliousandth the intensity of 

 light of the corresponding part of the object. But when 

 on this already faint part of the image I focus another 

 sixth inch objective I still further spread that light over 

 an area 360,000 greater and I get the 1-360, 000th of the 

 intensity of light with which such photomicrography has 

 hitherto been accomplished, \\m\ is, I have the 1-360,- 



