Early History of the Microscope. 5 



to a double convex lens of unequal convexities, almost reminding 

 one of a Coddington lens. 



Dr. Hooke, too, describes a method of placing his glass 

 globules in contact with water when examining that fluid, and 

 speaics of the clearness and brightness gained by this means. 



In 1702 we have Wilson's microscope. This was an alto- 

 gether more elaborate instrument, consisting of an object- 

 lens, an object-holder, a screw for focusing, and a condensing 

 lens. 



In 1738, Dr. Lieberkuhn made the greatest improvement the 

 single microscope received, and that, one which had from the 

 beginning been wanted, in that he placed the small lens in the 

 centre of a highly polished concave speculum of silver, which, by 

 reflecting light on to an opaque object placed underneath it, 

 opened up the possibility of examining such objects, thereby 

 placing a huge new field of research within the reach of micro- 

 scopical workers of the time. On this account I need hardly 

 point out this instrument obtained and maintained a high 

 reputation, so much so that nearly all the compound micro- 

 scopes subsequently made were by a simple device rendered 

 capable of, on occasion, supplying a Lieberkuhn's single micro- 

 scope. This great man made three forms, but I have only taken 

 two of them, as amply illustrating his invention. 



Then, in 1740, we find a somewhat elaborate single instru- 

 ment brought out by the elder Adams, which he called the 

 Universal Single Microscope ; the whole of the magnifiers were 

 mounted on a revolving wheel, by which means they might be 

 readily brought under a fixed eye-piece, which was also sup- 

 plied with a speculum for opaque objects, the whole being 

 mounted on a pillar and illuminated by a mirror. 



In 1742, Benjamin Martin, of Beading, invented a botanical 

 magnifier, which caused a good deal of interest at the time, and 

 is now largely used ; in fact, I suspect that at the present 

 moment many of us have a specimen of the instrument in our 

 pockets. 



In 1747, Cuflf the optician improved, at the suggestion of 

 Mr. Martin Folkes (who was President of the Boyal Society in 

 1742), the pocket microscope of Wilson, by fixing it to a stand, 

 and adding a mirror for illumination ; and subsequently further 

 improved it by mounting the lens on a moveable arm, and 

 making a stage to slide up and down on a square stem. This 

 ■was the instrument used by Mr. Ellis in his examinations of 

 corallines and zoophytes in 1756. 



Then we have the microscope invented by Dr. Withering, 

 consisting of three plates, the upper and lower of which 

 contained a lens ; the middle plate or stage was moveable on 

 the stout wires supporting and connecting the top and bottom 



