1796 



Journal of Applied Microscopy 



expensive, unless an outfit of objectives is included. The objectives used on 

 the regular laboratory microscopes are available for projection work. Solar 

 apparatus commends itself to beginners in projection, because of the ease with 

 which it is manipulated. 



There is a little confusion in the use of the terms porte-lumie're and heliostat. 

 While both consist, essentially, of a mirror which may be rotated so as to throw 

 a beam of light in a given direction and maintain it in a fixed position, the neces- 

 sary rotary movements are performed in the porte-lumiere by hand, but in the 

 heliostat by clockwork. 



The accompanying engraving shows a simple form of porte-lumiere with a 

 low priced projection microscope embodying suggestions by the writer. In decid- 

 ing on a location for the apparatus, if there is a choice of windows, it is well to 

 remember that the two most desirable conditions to be met are the maximum 

 number of hours of direct sunshine per day and the longest projecting distance, 



Fig. 2. — Simple Form ot I'ortelumicre and Microscope. ///, mirror ; />, plate; 

 //.handle; .r, mirror screw; 70, water cell; .>/>, springs; /« < , microscope 

 carrier ; </, rotary diaphragm ; .1 (, spring clips ; ;-, rack and pinion ; //, base 

 rods ; s s c, substage condenser ; a, amplifier. 



i. e., the distance from the porte-lumiere to the screen. Thirty feet is a good 

 distance and has the advantage of giving relatively high magnification when low 

 power objectives are used, such objectives being of most general usefulness on 

 account of their large fields and long working distances. The latter character 

 is necessary, because, as will be explained later, live animals and plants are 

 usually mounted in some form of glass cell containing water. 



A convenient method for mounting the apparatus in the window is to rut a 

 wide board to a length equal to the width of the window-sash. By removing a 

 part of the batten on one side of the window, the board is set in place under the 

 raised sash, which is then lowered until it rests upon the upper edge of the board. 

 If the board does not fit closely so that it can be shaken, it should be fastened 

 in place by common sliding bolts screwed to its inner side near the ends and 

 slipping into holes carefully located in the window-frame. The plate (p) of the 

 porte-lumiere is laid on the board and marks made to indicate the position of 

 the screw holes near the corners. A hole is then cut in the board large enough 

 to permit the mirror (m) and base rods (t) to be passed through and the plate is 



