104 THE MICROSCOPE. 



engines, embossed with an array of nuts, screws, handles, etc., truly 

 appalling to the beginner, and unnecessarily perplexing even to the 

 experienced veteran. In 1850 Professor Riddle of New Orleans in- 

 yented the stereoscopic binocular, which, though much improved 

 since that day, appears still to be open to these objections : loss of 

 light and more or less imperfection of definition. Thus, on the 

 whole, the effect of the invention of the " Binocular " seems to us to 

 have its parallel in that of the "Solar," while increasing the number 

 of interested lay observers, it has proved a stumbling block in the 

 path of the scientific investigator, who desires, above all things, the 

 improvement of the microscope as an instrument of precision. * 

 * * * The lenses which were believed to have so nearly 

 attained the limit of perfection fifteen years ago [resolving Noberts' 

 fifteenth band, /. e.^ lines 1-91, 000th of an inch apart] are antequated 

 now, and the theoretical limit of perfection has thus moved forward 

 and forward like the horizon, and seems destined ever to recede. 

 Thus, Surgeon-General Woodward of the navy has since resolved 

 the entire nineteenth band on the same plate. * * * * 

 Ten years ago Mr. Tolles began the now famous aperture war by 

 the publication of his article on experiments on angular aperture, in 

 the London Monthly Microscopical Journal, his advocacy of the wide- 

 angle theory being antagonized by such famous opticians as Messrs. 

 Wenham and John Mayall, Jr., — and peace was not declared until 

 Mr. T. had constructed and furnished the formulae of his two and 

 three system balsam immersion objectives with apertures ranging 

 from 100° to 110° — backed by the mathematical demonstrations of 

 Mr. Renel Keith and Dr. Piggott. And four years ago Prof. Stokes, 

 of Cambridge (England), demonstrated, mathematically that an aper- 

 ture of 180° in glass was conceivable — while Zeiss and Powell and Le- 

 land, in Europe, as well as Tolles, Spencer, Gundlach and Bausch, in 

 this country, are at this very time constructing homogeneous immer- 

 sion objectives of 136" to 140° balsam angle. The lesson, then, that I 

 would draw from this glorious history of struggle with and triumph 

 over almost insurmountable obstacles is: the end is not yet; absolute 

 perfection can never be achieved, but may be constantly approached ; 

 the horizon of yesterday is the halting place of to-day. The future 

 holds for the coming optician triumphs as brilliant as any of those 

 in the past, and the time will come, nay is perhaps close at hand, 

 when the best microscopes of to-day will be as antiquated as those 



