The Microscope. 33 



TECHNOLOGY. 



THE LATEST CAMERA LUCIDA OF ABBE. 



'^ EISS makes two fonxis of the new Abbe camera liicida. Both 

 '-^ are constructed on the same principle, but one (No. 70) has 

 a large mirror and a longer arm than the other (No. 09). The larger 

 form, the one recommended by Dr. Mayer, is only made to order. 

 The advantage of this form is that it enables one to utilize the whole 

 field of vision without any perceptible distortion of the image, and 

 is thus especially useful in drawing comparatively large objects with 

 low powers. With the smaller camera (No. 69) the whole field can 

 be projected on the drawing-paper only by giving the mirror an 

 inclination differing so much from the angle (45*^), required for 

 accurate drawing, that the image is more or less disproportioned. 

 The Abbe camera is superior to that of Oberhiiuser in two important 

 particulars: it gives a much larger field of vision and better light. 

 Its construction does not admit of use with the microscope-tube in a 

 horizontal position. This is a defect which ought to be at once cor- 

 rected. The Abbe camera, especially the larger one, can be used to 

 great advantage with the embryograph of His. It is only necessary 

 to add to the stand a horizontal arm, to which the camera can be 

 fastened. 



The construction of the Abbe camera is illustrated in the accom- 

 panying cut. 



The drawing surface is made visible by a double retiection from 

 a large, plane mirror, and from the silvered surface of a small prism 

 in the usual point of the eye-piece. The microscopic image is seen 

 directly throu.gh an apparatus in the silvering of the pi'ism. By the 

 concentricity thus obtained of the bundle of rays reaching the eye 

 from both the microscope and the paper, the image and pencil are 

 seen coincidently without any straining of the eyes. With this 

 apparatus, moreover, drawings may be executed on a horizontal sur- 



