ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 135 



been able to make I imagine (my fine-adjustment not being graduated 

 there is no attempt at complete accuracy) that the distance through 

 which the 1/4 in. objective passes from the true focus to the lower 

 position is not more than the 1/150 in. ; and from the true focus to the 

 higher position about the same, or rather less. This is accomplished by 

 a very slight tnrn indeed of the milled head of the fine-adjustment. 

 In the case of Gonium pectorale it is usually pretty clear when one has 

 the plant properly in focus, especially as the view of the flagella comes 

 as a guide. But there are many objects as to which it may be supposed 

 that so small a difference as 1/150 in. may not seem to throw them out 

 of focus, whilst in reality they are so to an extent which might cause 

 error. Query : might the striee of diatoms come under such a category? 

 It is a common thing to hear and read that the appearances of things 

 under the Microscope are not always to be taken as strictly true ; and 

 doubtless the microscopists of old days owed some of the queer figures 

 they drew to this cause. The changing colours and form of Gonium 

 pectorale as above noticed may perhaps serve a useful purpose, if they 

 warn some young microscopists to be very particular in the observations 

 they make ; possibly also some older hands might take a hint." 



Penny, K. G. — Microscope Objectives — Angular Aperture. 



Engl. Mech., XLVIII. (1888) p. 316. 



C6) Miscellaneous. 



Death of Dr. Zeiss. — We deeply regret to have to record the death 

 of Dr. Carl Zeiss, the eminent Jena optician, who in conjunction with 

 Prof. Abbe has done so much to advance the practical construction of 

 objectives. His name will for many generations be associated with the 

 most important epoch of Microscopy ; the epoch in which the famous 

 ditiraction theory of Prof. Abbe was promulgated which revolutionized 

 microscopical optics, to be succeeded by the important suggestion of 

 our late Treasurer, Mr. J. W. Stephenson, which resulted in the homo- 

 geneous-immersion objectives first made in 1878, and later followed by 

 the still further advance shown by the construction of apochromatic 

 objectives. In the practical construction of these and the homogeneous- 

 immersion objectives the deceased played a leading part, and whilst it is 

 impossible to exaggerate the services which Prof. Abbe has rendered to 

 microscopy in these matters, he would, we are sure, be the first to admit 

 the invaluable assistance he received from Dr. Zeiss. 



The remarks of the President and others on Dr. Zeiss's death will 

 be found at p. 162. 



Death of Mr. Zentmayer. — The following is the report of the Com- 

 mittee of the New York Microscopical Society, which was appointed, 

 more Americano, to draft resolutions relative to the death of Mr. Joseph 

 Zentmayer : — 



" Whereas this Society has received with sorrow the announcement 

 of the death of Mr, Joseph Zentmayer, which occurred at Philadelphia 

 Pa., on March 28th, 1888, it is hereby * 



" Eesolved : — 



" 1. That in the death of Mr. Joseph Zentmayer the labourers in the 

 various branches of science employing optical instruments have lost the 

 inspiriting presence and helpful co-operation of an eminently intelligent 

 and successful author, inventor, and mechanician, whose knowledge of 



