ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 491 



recorded. Thus a Zeiss 2 mm. objective,~with projection ocular 4, and 

 a camera length of 29| in., measured from the Microscope stage to the 

 sensitive plate, required a — 5 D lens. 



Different planes in a thick object are photographed by focussin" the 

 Microscope upon the same point in the object, and employing spectacles 

 of various negative strengths. 



In illustration of the paper, there is a plate containing nine photo- 

 micrographs of one section of an egg of Allolobophora foetida, showing 

 the lower pole of the first maturation spindle, and two and a half of 

 the eleven chromosomes. 



The following passage, which is extracted verbatim, throws a curious 

 side light upon the efficiency of the Continental model Microscope, 

 with its direct-acting screw fine adjustment, when used for rough and 

 ready cytological photomicrographic work. 



" It is a waste of time to expose the plate unless the stability of the 

 focus is assured, for the slightest change of focus during exposure de- 

 stroys the sharp outlines of the image, giving that blurred effect so 

 familiar in many photomicrographs. This slipping of the focus we 

 have found the most troublesome factor in photography, and this danger 

 must exist whether the vertical or horizontal camera is used, or with 

 any method of focussing. 



" A worn or an imperfect micrometer screw is not the sole cause of 

 this trouble, for we have tested a new Zeiss Microscope and we found 

 the focus changed so radically that after a half hour's wait, the centro- 

 some (on which the test was made) was completely lost sight of. We 

 are inclined to think that changing of the focus is due rather to varia- 

 tions of temperature to which the Microscope may be subjected, for 

 example, in bringing it from a warm part of the laboratory and placing 

 it close to a window, though this would seem hardly adequate to account 

 for all the vagaries of a changing focus. Sometimes a wait of an hour 

 or more is needed to ensure a stable focus, but fortunately these are rare 

 occasions, as a rule ten or fifteen minutes test is all that is needed." 



Photomicrographic Device.* — F. E. Ives describes a simple home- 

 made arrangement for securing a photograph of the microscopic image 

 without any readjustment and even without interfering with the inclina- 

 tion of the instrument, 



A half-inch mahogany box-lid 10 in. wide and 12 in. long served as 

 a base for the Microscope, which was held securely in place by means 

 of stops against which it was pressed. A small shelf-bracket was fixed 

 on each side of the Microscope so that one of the screw-holes in the 

 bracket came exactly opposite the centre of the Microscope joint. The 

 brackets were so separated as to just sufficiently clear all the working 

 parts of the Microscope. The screw-holes are the points of attachment 

 for the camera device and must occupy such a position in order that the 

 camera may swing from the same centre as the Microscope body, and 

 thus be adjustable by a single movement for any desired inclination. 

 On a double-pillar Microscope the camera attachment could be adapted 

 to swing from the centres on the Microscope itself, and the brackets 

 could be therefore dispensed with. The camera was a simple box with 

 a lens at one end and a plate-holder at the other — the lens of 10-in. 



* Journ. Franklin Institute, cliii. (1902) pp. 371-6 (2 figs.). 



2 K 2 



