CONSTRUCTION AND MANAGEMENT. 



165 



Fig. 28, — MusccE volitanies. 



known as Flying Flies, represented in Fig. 28. These "are more 



visible and tenacious one day than 

 another ; a brilliant light or physical 

 fatigue renders them more apparent. 

 We sometimes perceive these flies with 

 ordinary light, when looking up at the 

 sky, or at a strongly illuminated sur- 

 face, such as the ground covered with 

 snow. At other times, notwithstand- 

 ing the most fatiguing examination 

 of diatoms, we have remained for en- 

 tire weeks without being aware of their 

 existence." 



In Book IV. we have : Chapter i, 

 General Rules for preparing micro- 

 objects, with descriptions of the 

 various Aqueous and Oily, Resinous 

 and Chemical, media ; Chemical and 

 Staining Reagents, and instruments used in the preparation of 

 objects, etc., etc. Chapter 2 is entitled the Microscopist's Lib- 

 rary, in which the author has " collected together a number of 

 books which the microscopist, and especially the botanical micro- 

 scopist, may, with advantage, consult," but judging from the very 

 meagre list, Foreign and English (about three dozen works are 

 named), we cannot think his library is overdone with periodical 

 literature, as neither the Journal of the Qiiekett Club^ nor our 

 own Journal, are mentioned, nor are the Aj?ierkan Month/y 

 Microscopical Journal or The Microscope. 



Book V. treats of the microscope in the past and in the future. 

 Here, we are told, "an early form of microscope consisted of a 

 magnifying glass set in a mount, and carried on a small foot. A 

 needle was fixed at a short distance from the lens, and the object 

 for examination was stuck on the point of a needle. It was this 

 sort of microscope which gave rise to the microscope of Leeuwen- 

 hoeck, and with which this illustrious microscopist made his 

 splendid discoveries. 



Leeuwenhoeck's microscope. Figs. 29 and 30, differed from that 

 above described in the perfection of his lenses, which magnified 



