SCIENCE AS MEASUREMENT 93 



on the optics of astronomy, now (1611) produced 

 his Dioptrice, the first satisfactory statement of the 

 theory of the telescope. 



About 1639 Gascoigne, a young Englishman, in- 

 vented the micrometer, which enables an observer to 

 adjust a telescope with very great precision. Before 

 the invention of the micrometer exactitude was im- 

 possible, because the adjustment of the instrument de- 

 pended on the discrimination of the naked eye. The 

 micrometer was a further advance in exact measure- 

 ment. Gascoigne's determinations of, for example, 

 the diameter of the sun, bear comparison with the 

 findings of even recent astronomical science. 



The history of the microscope is closely connected 

 with that of the telescope. In the first half of the 

 seventeenth century the simple microscope came into 

 use. It was developed from the convex lens, which, 

 as we have seen in a previous chapter, had been 

 known for centuries, if not from remote antiquity. 

 With the simple microscope Leeuwenhoek before 

 1673 had studied the structure of minute animal or- 

 ganisms and ten years later had even obtained sight 

 of bacteria. Very early in the same century Zacharias 

 had presented Prince Maurice, the commander of the 

 Dutch forces, and the Archduke Albert, governor 

 of Holland, with compound microscopes. Kircher 

 (1601-1680) made use of an instrument that repre- 

 sented microscopic forms as one thousand times larger 

 than their actual size, and by means of the compound 

 microscope Malpighi was able in 1661 to see blood 

 flowing from the minute arteries to the minute veins 

 on the lung and on the distended bladder of the live 

 frog. The Italian microscopist thus, among his many 



