228 



SCIENTIFIC THOUGHT. 



25. 



The Micro- 

 scope. 



cess of fecundation in plants, and from Martin Barry to 

 Hertwig and Fol on that in animals, has been brought 

 to a temporary climax. The combination of telescope 

 and microscope in the spectroscope has opened out a 

 field of research in astronomy of which Laplace had 

 no conception. 



So much has depended, during our century, on the 

 unravelling and disentangling of the imperceptibly small 

 (once considered an unworthy occupation), that a short 

 reference to the history of that optical instrument to which 

 we are so greatly indebted may not be out of place. 



The gradual perfection of the microscope is as much 

 indebted to the problems and labours of anatomical 

 workers during the seventeenth and the nineteenth cen- 

 turies, as anatomy itself reciprocally has been indebted 

 to the microscope. Robert Hooke, in 1660, first gave a 

 useful form to the compound instrument. Leuwenhoek 

 perfected the simple microscope ; and during the earlier 

 part of our century no one did more than Amici in 

 Modena and Lister in England l to start that great suc- 



Fol, 0. Hertwig, and others, 

 showed that one of the essential 

 phenomena in fertilisation is the 

 intimate and orderly association 

 of the sperm-nucleus, of paternal 

 origin, with the ovum - nucleus, 

 of maternal origin, the result 

 being the cleavage or segmentation- 

 nucleus. The researches of Stras- 

 burger, De Bary, and others, 

 established the same result in 

 regard to plants" (J. A. Thom- 

 son, ' The Science of Life,' p. 

 127, 1899). 



1 The improvements of Amici 

 seem to go back to the year 1812, 

 those of Lister to 1826. The for- 

 mer is usually considered the in- 



ventor of the "immersion " system, 

 that of placing a drop of water 

 between the object or its covering 

 glass and the objective lens. This 

 system has lately been improved by 

 Abbe, who discovered a liquid with 

 the same refractive index as the glass 

 of the objective possesses. Accord- 

 ing to Hogg (' The Microscope,' 

 15th ed., 1898, p. 10), the immer- 

 sion system was suggested by Prit- 

 chard in London before Amici hit 

 upon it. The necessary modifica- 

 tions required where the immersion 

 system is used, seem, however, to 

 have been first worked out by 

 the celebrated Paris opticians, MM. 

 Hartnack and Nachet. 



