1880.] 



MICROSCOPICAL JOURNAL. 



91 



same high-angled, homogeneous- 

 immersion lens, shows decidedly 

 more force of definition than the 

 one having a lower angle. 



In 1878, Dr. J. J. Woodward made 

 a series of micro-photographs of 

 Amphiplura pellucida, mounted in 

 balsam, with a Zeiss -^ and ^inch 

 oil-immersion, together with other 

 notable objectives for comparison 

 of their respective merits. Among 

 these lenses were a \ and yVi'ich 

 by Spencer, glycerin-immersion, 

 and a ^g-i^^ch oil-immersion by 

 Tolles. It is only necessary for 

 any unprejudiced person to examine 

 this series of photographs to decide 

 at once as to the superiority of the 

 homogeneous-immersion lenses in 

 defining power, with the exception 

 of the Zeiss -|^-inch, over others used 

 in this trial. Since that comparison, 

 Mr. Tolles has brought out a new 

 homogeneous-immersion ^inch ob- 

 jective of nearly 127° interior-angle, 

 measured in a medium, the same as 

 Prof. Abbe uses, of 1.50 refractive 

 index. 



One of these new series, the sec- 

 ond that Mr. Tolles had made, I 

 obtained some three months ago, 

 and I have subjected it to a variety 

 of tests and am becoming every 

 day more anci more attached to it. 



This truly wonderful lens posses- 

 ses a greater variety of noticeable, 

 excellent qualities, than any that 

 has as yet come under ray observa- 

 tion ; such as will, I am confident, 

 be fully appreciated by the working 

 microscopist ; and more especially 

 such as work on histological prepara- 

 tions, or desire to observe biological 

 phenomena by the aid of high mag- 

 nifying power and excellent defini- 

 tion. The angle of the lens is the 

 highest yet attained. The correc- 

 tions are such as yield results sur- 

 passing anything I have heretofore 

 been able to get with other objec- 

 tives of high angle, as weU as oil- 



immersions of very high interior- 

 angle. 



The definition of the transverse 

 striae of Amphiplura pellucida by 

 lamplight, with a hemispherical lens 

 as an immersion illuminator, is very 

 sharp and approaches nearer to the 

 resolution obtained by sunlight 

 and blue-cell illumination than any- 

 thing I have ever seen. The striae 

 show distinctly with a two-inch eye- 

 piece and no amplifier. 



From this point the power can 

 be increased by a i-inch eye-piece 

 and an amplifier, — the lines still 

 visible and appearing like pickets 

 on a fence. This testing affords an 

 admirable practice for the micro- 

 scopist, and teaches him how to get 

 the best results with his objective 

 and how to manage the illumination 

 properly, which must be learned by 

 practice ; such practice ought not 

 to be sneered at by students of his- 

 tology. 



If, now, we wish to test the bril- 

 liant definition of this new ^ on 

 histological preparations, it matters 

 not what specimen we select, the 

 result is always an improvement 

 over results obtained with lower 

 angled objectives. But my favorite 

 object for this purpose is a prepara- 

 tion of the tail of a newt, which I 

 prepared to illustrate the so-called 

 "giant nuclei," but more especially 

 the arrangement of the bioplasm in 

 the nuclei of the epithelial cells, 

 which, when taken at the proper 

 time, exhibit the dividing nuclei. 



This object affords a fine oppor- 

 tunity to demonstrate the masterlv 

 skill and care that Mr. Tolles has 

 bestowed on this new ^, as well as 

 to show the preeminent manner in 

 which these high-angled lenses ex- 

 hibit olijects by central and slightly 

 oblique illumination. When this 

 object is examined with an ordinary 

 low-angled water-lens, an amateur 

 would be easily misled into the be- 



