1900] MICROSCOPICAL JOURNAL. 251 



ble rest on the felt and do not come into contact with the 

 wood at the side. There is another cause of blurring of 

 the image, namely, a faulty connection between the fine 

 adjustment of the microscope and the long-focussing rod 

 which runs by the side of the camera. Rubber bands of 

 any description are not a success. 



In last year's Annual is a short description of the me- 

 chanical contrivance made by the writer, which is being 

 used daily. It responds readily to the touch on the focuss- 

 ing rod, and, when a sharp image is obtained, keeps per- 

 fectly steady. 



A shifting focus, due to the expansion and contraction 

 of the apparatus from varying degrees of temperature, has 

 never given me any trouble, although all work is done in 

 the winter about six feet from the fireplace with a good 

 fire burning, the camera and microscope being set up each 

 time and work begun without waiting for the parts to be- 

 come uniformly warm. 



Lime-light is exceedingly useful for high-power work, 

 such as the photography of bacteria at one to four thous- 

 and diameters, but at one thousand diameters it is not es- 

 sential, for an oil lamp with an inch wick used edge-on 

 will fully expose a medium orthochromatic plate in from 

 one to two minutes, using a 1-1 2th apochromatic objective, 

 and Zeiss' No. 4 projection ocular. 



The writer always uses a blow-through jet and Zircon- 

 ium lime for the higher magnifications up to four thous- 

 and diameters. Photography at this power is not often 

 necessary or useful, and when the occasion arises one can 

 easily sit down and wait during the ten or fifteen min- 

 utes which are required for exposing the sensitive plate. 

 It seems to me that better results are obtained by using 

 a medium power illuminant and giving a little longer ex- 

 posure, than by using the brightest possible light with 

 quick exposures. 



For fine low-power work the blow-through jet is of ten 



