APPENDIX. 283 



thes, have all shown similar phenomena. These species 

 are all of very minute dimensions. It will probably 

 not be unwelcome to our readers if we give them some 

 of the principal results which have been obtained from 

 the study of these curious animals. 



Leuwenhoeck *, Baker f, and Spallanzani J, made their 



* Leuwenhoeck, who was born at Delft, in Holland, in 1 632, and 

 died in 1723, is justly regarded as the founder of micrography. 

 His long life was devoted to the study of the world of infinitesimal 

 beings, and to the improvement of the instruments adapted for 

 these observations. The compound microscopes known in his day 

 were very imperfect, and subject to many errors, which induced 

 Leuwenhoeck to employ only simple microscopes, that is to say, very 

 small lenses of short focal lengths, which he made himself, and 

 fixed between two plates of metal, that had been pierced with a 

 very narrow opening. Each instrument was only intended to serve 

 for a small number of objects, and Leuwenhoeck always kept a 

 great many of these glasses by him in readiness for use. The 

 collection of these microscopes, which he bequeathed to the Royal 

 Society of London, consists of twenty-six plates, all provided with 

 their several lenses. It was by means of these simple instruments, 

 that he made those numerous observations which have won for him . 

 a European reputation. During his stay in Holland, Peter the 

 Great came to visit him, and by way of acknowledgment of the 

 honour done him, the micrographer showed the czar the circulation 

 of the blood in the tail of an eel. Notwithstanding his assiduous 

 labours Leuwenhoeck preserved excellent sight to the end of his 

 life a blessing which has not been the lot of all his imitators. 



f Henry Baker was born in London, and died in 1774. He was 

 one of the precursors of the Abbe de 1'Epce, but while he devoted 

 his attention to the discovery of methods for teaching deaf mutes 

 the art of speaking, he also made many micrographical observations, 

 and Spallanzani speaks of him in terms of high commendation. 



% The Abbe Spallanzani, who was one of the most remarkable 

 savants of the eighteenth century, was born at Scandiano, in 1729, 

 and in early life distinguished himself by his literary acquirements, 

 while he also held the chair of Logic, Metaphysics, and Greek 

 Philosophy at Reggio. He soon, however, devoted his attention 



