4 HISTORY OF THE MICROSCOPE. 



same ingenious author invented another water-microscope, consisting 

 of two drops of water separated in part by a thin brass plate, but 

 touching near the centre, which were thus rendered equivalent to a 

 double-convex lens of unequal convexities. 



Dr. Hooke described the method of using this single microscope : 

 " If you are desirous," he says, " of obtaining a microscope with one 

 single refraction, and consequently capable of procuring the greatest 

 clearness and brightness any one kind of microscope is susceptible of, 

 spread a little of the fluid you intend to examine on a glass plate ; 

 bring this under one of your microscopic globules, then move it gently 

 upwards till the fluid touches the globule, to which it will soon adhere, 

 and that so firmly as to bear being moved a little backwards or for- 

 wards. By looking through the globule, you will then have a perfect 

 view of the animalcules in the drop." 



The construction of the single microscope is so simple, that it is 

 susceptible of but little improvement, and has there- 

 fore undergone few alterations ; and these have been 

 chiefly confined to the mode of mounting it, or to 

 additions to its apparatus. The greatest improve- 

 ment this instrument has received was made by Dr. 

 Lieberkuhn,* about the year 1740 : it consists in 

 placing the small lens in the centre of a highly- 

 polished concave speculum of silver, by which means a 

 strong light is reflected upon the upper surface of an ob- 

 ject, which is thus examined with great ease and pleasure. 

 Before this contrivance, it was almost impossible to exa- 

 mine small opaque objects with any degree of exactness 

 and satisfaction; for the dark side of the object being 

 next the eye, and also overshadowed by the proximity of 

 the instrument, its appearance was necessarily obscure 

 and indistinct. 



Lieberkuhn adapted a separate microscope to every 

 object : but all this labour was not bestowed on trifling 

 objects; his were generally the most curious anatomical 

 preparations, twelve of which, with their microscopes, are 

 deposited in the Museum of the Royal College of Sur- 

 geons. 



fig- 1. Lieberkuhn's instrument, fig. 1, is thus described by 

 Professor Quekett : -)- a b represents a piece of brass tube, about an 



* Dr. Nathaniel Lieberkuhn of Berlin. 



f Practical Treatise on the Microscope, p. 16. 



