Boss's New One-Twelfth. 129 



lens in closer proximity. Now, if you receive through a given 

 glass all the ossilike light, and the corrections are extremely 

 fine, it is obvious that you can raise the magnifying power by 

 eye-pieces to the highest practical extent ; that is to say, you 

 can magnify your object as long as all the light it can emit with 

 a given illumination enables you to see it. Of course, in 

 pushing the power of a glass in this way it is exposed to the 

 severest test ; and Mr. Thomas Ross can desire no higher tes- 

 timony to his skill than the fact that both Mr. Brooke and Mr. 

 Lionel Beale have seen extremely minute and very delicate ob- 

 jects with the new gth in a manner that has not been surpassed 

 by the performance of any other glass. 



We are indebted to the courtesy of Mr. Ross for an oppor- 

 tunity of trying two of the new ^ths upon a variety of objects 

 and under different conditions, and we can emphatically endorse 

 the very high praise they have received from other observers. 

 They are managed with great facility, the definition is exqui- 

 sitely sharp and clear, and the penetration large in proportion 

 to the angular aperture they possess. What more can be de- 

 shed ? For a great many purposes we say nothing more can 

 be desired, until new materials are at the disposal of the 

 optician, or some novel and unexpected optical formula is 

 devised. 



Messrs. Powell and Lealand's ^th is so beautifully cor- 

 rected as to leave very little possibility for improvement in this 

 respect ; but Mr. Ross may still be right in the opinion that 

 minute glasses in the front of any combination tend to introduce 

 certain errors of diffraction, and that, in stopping at his ^th, 

 he is able to keep these errors down. When two great artists, 

 such as Ross and Powell, both do their best, we cannot expect 

 the balance of merit will be easy to discern ; and it would re- 

 quire a prolonged and very elaborate series of experiments to 

 determine whether everything that can be shown with the 

 ^th can also be shown with ^th when raised to the same power. 

 It is, however, certain, that if there be cases in which the 

 ^th would surpass its rival, they must be very few. The fore- 

 most obstacle to the use of the 2 ^th, and which does not affect 

 the ]|th, is the closeness of its approximation to the object. It 

 cannot be worked through glass that will bear handling, and 

 consequently it is better adapted for the display of a carefully- 

 prepared object, than for research under the usual difficulties 

 which the examination of tissues, etc., entails. 



In a former paper we praised Smith and Beck's ^th as an in- 

 strument of research. Its form (that of a dialyte) probably 

 does not admit of the very finest corrections that are possible; 

 but it has an excellent definition, great penetration,wovk& through 

 glass of the thickness suited to Ross's ^th, and from the mode- 



