278 THE AMERICAN MONTHLY [December, 



ments, as shown by each one of them at their respective dates, were re- 

 markable. About 1750 appeared Adams's Solar Microscope, for trans- 

 parent and opaque objects, and these are now considered beautifnl 

 specimens of rare solar microscopes. Adams made a number of forms 

 wdiich are figured in his " Essays on the MicroscojDe," London, 1787. 



During the years 1750 to 1800 makers of microscopes were numer- 

 ous, the most distinguished makers being Cuff, Ellis, Dolland, Martin, 

 Adams, and Dellebarre ; the works of these men speaking of difficult 

 investigation, originality, and marked progress. 



Cufi"'s models were much sought in their day and were considered 

 very serviceable working instruments. The fine adjustment was of 

 great delicacy and showed that Cuff spent much labor in the imj^rove- 

 ment of the mechanical constructioij. 



The period of achromatism as applied to the microscope, about 1820, 

 marks a period in the history of the instrument from which one can 

 readily observe the great advance made in the perfecting of the instru- 

 ment, both optically and mechanically. Great changes took place in 

 the construction, with particular reference to the means of focusing. 

 This period may be reckoned as the dividing time between the two 

 classes of instruments, namel}', the ancient, those made prior to the 

 date of achromatism, and the modern, those constructed subsequently. 



In 1824 Tully constructed an achromatic microscope, and he applied 

 mechanical motion to the stage of the instrument. 



Amici, Selligue, Chevalier, and Merz seem contemporaneous, and 

 represent microscopes of the achromatic type between 1820 and 1835. 

 In the history of this instrument from this date on to the present year 

 the names of Oherhaeuser, Hartnack, Zeiss, Reichert, Nachet, Powell, 

 and Leland, Grubb, Zentmayer, Tolles, Bulloch, Beck, Ross, and 

 Swift will ever stand out as memorials, and mark distinctive epochs 

 of advancement. During this period inventions of every description, 

 different forms of stands, innumerable accessories, achromatic conden- 

 sers, mechanical stages, a variety of new lenses, both dry and immer- 

 sion, adjustable and non-adjustable, and new forms of oculars, have 

 been introduced in a whirl. Many of these proved of little value, some 

 were but the stepping-stones to valuable future improvement, while 

 mam' will prove of everlasting benefit and service. To repeat Mr 

 Wilson : " It would be quite impossible to pass in review the many ex- 

 cellent types of microscopes designed since the introduction of achro- 

 matism, and the progressive stages by which our grand instruments 

 have been undergoing a gradual process of evolution from the primitive 

 ones. Suffice it to say, that the advance in the construction of the in- 

 strument has been steady and continuous from the earliest known simple 

 model by Tulley, with its struts connecting the base with the body-tube 

 as a support, to the handsome and perfect instruments of the present 

 day, embracing every possible adjustment that is known to make it 

 suitable for all purposes of investigation." 



It may be of interest to you to know that, contained in the Army 

 Medical Museum, in this city, there is a collection of ancient and mod- 

 ern microscopes, numbering at pi'esent about 175 instruments of all 

 forms, where you may observe the progressive stages by which the in- 

 strument has grown to its present state of perfection. 



