and Laboratory Methods. 2147 



metal diaphragm having a circular opening of the proper size to admit the beam 

 of light from the mirror into the condensing system of the microscope. A 45° 

 prism placed upon the top of the microscope tube serves the purpose of reflect- 

 ing the vertical beam to a horizontal path. With the projection microscope the 

 illumination is sufficient for use with powers up to and including one-half inch 

 with ordinary screens at the same distance that the projection lens is ordinarily 

 used, and with undiminished circles of light. 



The great advantage of the horizontal position for preparations of living 

 forms such as Paramoecium, Gammarus, Entomostraca, Amceba, Vorticella, and 

 other infusorial forms, as well as any other microscopical thing in fluid which it 

 is desired to show, as, for example, urinary deposits, crystals, etc., is apparent. 



The optical bench, as above described, is mounted upon a three-legged iron 

 support so that it may be rotated completely around, and this mounting can be 

 used for photomicrography as well as for projection work, being in this case 

 attached to the complete photomicrographic camera as shown in Fig. 8., the 

 microscope being swung out of the optical axis when it is desired to arrange the 

 object in the field and for preliminary focussing, as shown in Fig. 9. This con- 

 struction can be taken advantage of in the lecture room by having the photo- 

 graphic dark-room situated at the rear of the lecture room provided with a 

 window opening onto the lecture room. The camera and optical bench can be 

 lined up at the side of the dark-room next to the lecture room and the whole 

 apparatus used for photomicrography when desired. When the optical bench 

 only is desired for projection, the window can be opened, the optical bench 

 turned through 90° so as to project its image upon the screen, and both vertical 

 and horizontal attachments can be used without difficulty in this manner. This 

 projection apparatus can also be used to great advantage for making bromide 

 enlargements, both from lantern slides and from microscopic objects to be used 

 as charts. Any points to be emphasized can be worked up on such enlarge- 

 ments with crayon or pencil after the enlargements have been made, and any 

 portions can be colored with analin or water colors. This is a field of work 

 which such a projection apparatus will greatly facilitate, and one which has as 

 yet been very little developed. It is believed that this construction will lend 

 itself particularly well to physical and chemical demonstration work, and the 

 special accessories for these uses which are now in process of development will 

 form the subject of another paper. L. B. Elliott. 



