292 RAMBLES OF A NATURALIST. 



by suffering a very small drop to fall upon an opening 

 cut in a metallic plate. The liquid, which of itself 

 assumed a somewhat spherical form, was thus, for a time 

 at least, able to serve in the place of a lens. Canada 

 balsam, turpentine, and several different varnishes were 

 also employed for the same purpose. 



One of those chances of which superior minds alone 

 know how to avail themselves secured to the microgra- 

 phers of the day that of which they had so long been in 

 search. In 1665, a young Dutchman, named Hartsoeker, 

 when holding a glass thread in the flame of a candle, 

 perceived that the melted extremity assumed a spherical 

 form.* Hartsoeker who had seen Leuwenhoeck manufac- 

 ture lenses, now attempted to place his own little spheres 

 of glass between two pieces of lead, through which he 

 made an apei^ture with the point of a pin ; on observing a 

 hair with this instrument he discovered to his great joy 

 that he was the possessor of a capital microscope. From 

 that time microscopists very often employed Hartsoeker's 

 method, and Le Baillif, amongst others, enjoyed for a 

 long period of his life a great reputation for his skill 

 in arranging such glasses. 



All the lenses of which we have spoken present great 

 inconveniences, for their use is fatiguing to the eye, the 

 field of view is very limited, and the magnification is 

 never very great. In 1813, the celebrated English 



* Hartsoeker, who was born in 1647, and died in 1725, was only 

 eighteen years of age when he discovered the art of constructing 

 simple microscopes with a glass thread. This discovery has, how- 

 ever, been disputed, and some authors have ascribed it, perhaps 

 justly, to the celebrated English mathematician Hooke, to whom 

 we owe the invention of portable watches. Hartsoeker made use of 

 the globules to prosecute some very interesting inquiries, and he 

 contests with Leuwenhoeck the claim to the discovery of those 

 animalcules which since their time have been found to exist in the 

 generative fluid of all animals. 



