MICROSCOPIC OBJECTS. 21 



Dr. Goring employed the late Mr. W. Tulley to make 

 him an achromatic object-glass for his microscope, and 

 consulted thereon the father of that artist, the celebrated 

 Charles TuUey'j who gave it as his opinion that the 

 time and money bestowed upon the attempt would be 

 wasted. Notwithstanding this, Dr. Goring, with signal 

 liberahty, engaged Mr. Tulley on the work. 



Though such was the opinion of the first optician of 

 the day, so httle was the subject understood, that at the 

 time Dr. Goring was engaged with this achromatic, on 

 his mentioning the circumstance to a friend who had 

 made important mathematical investigations in optical 

 matters, and who now occupies a place in the first rank 

 of science, the reply he received was, " I thought all 

 the best compound microscopes were achromatic " ! 



While this attempt was in progress, (for it occupied 

 some months, Mr. TuUey working in the day and 

 Dr. Goring tr}^ing them by night,) Dr. G. discovered 

 that the structure of certain bodies could be readily seen 

 in some microscopes and not in others. These bodies he 

 named Test Objects ; a full account of which will be 

 found in this work. Dr. Goring determined to try the 

 new achromatic on these tests; and was then led to the 

 all-important discovery, that the penetrating power of a 

 microscope depends upon its angle-of -aperture. This 

 explained the cause of all the former failures. It also 

 clearly indicated the right direction in which improve- 

 ments would result. From this time the superiority of 

 the achromatic construction over the ordinary compound. 



