THE president's ADDRESS. 361 



micrography, especially if a | cone of illumination is employed, 

 with a wide angled oil immersion objective. 



The connection of the focussing rod to the fine adjustment is 

 necessarily more complex with a lateral screw than with an 

 axial one, and on that account the axial movement may be con- 

 sidered preferable. 



We now come to the illuminant, which is so important that 

 several small details are unavoidable. There can be no doubt 

 that oxy-hydrogen is a veiy, if not the most, suitable light for 

 the purpose, for as to brightness there is enough and to spare, 

 it is rich in actinic rays, it is thoroughly under control, it is 

 inexpensive, it is perfectly safe ; the last, but perhaps the most 

 important, point is that it can be made small in size. 



With regard to the brightness it should be remembered t]iat 

 six seconds and nine seconds can be more easily and more 

 accurately timed than one second and one-and-a-half seconds, 

 and with regard to the size it is not difficult to maintain a 

 steady incandescent spot of lime quarter of an inch in diameter. 

 For this purpose we have a common mixed jet with a small 

 bored nozzle, fitted with the two usual taps and a common lime 

 holder. The only thing peculiar about the jet is its flatness in 

 front ; this is to allow a short focussed lens to be placed close 

 to it. The post to which the jet is attached is very massive, 

 and the post is fastened to a heavy lead stand ■ (weight 10 lbs.) 

 resting on three points, having a large ventilating hole cut in 

 it. This stand also forms the bottom of a small japanned tin 

 lantern (G : x 4| and 6|- high). The lantern has a door opening 

 on the left hand side of the board, and the front, which has a 

 removable tube fitting, can slide vertically. This lantern rests 

 on a solid block of wood, which also rests on the board on three 

 points. This block of wood holds also the heat interceptor, 

 which is a plain water trough 2 inahes thick with glass sides. 

 You will observe that nothing throughout the apparatus is 

 fixed ; the only thing which occupies an approximately definite 

 position is the microscope, which, of course, must be placed so 

 that the fine adjustment cord can pass over the head of the 

 fine adjustment screw ; also its position in- azimuth must be 

 arranged so that the image will be projected in a line with the 

 board. The microscope is so placed on the board that when 

 you are looking down the tube the board is on your right hand. 



