712 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



and are to be disregarded. The instrument is now revolved until the 

 long meridian lines of the images show a single straight and unbroken 

 one. If there is no astigmatism this condition will be seen at all axial 



Fig. Ii2. 



positions; if astigmatism, at but two positions. Directions are given, 

 for reading the variation of cornea curvature in dioptres and fractions. 



S^S8|ksife»fe3g^ 



■ flfip 





"\ 





Fig. 143. 



Interesting' Extracts from Borelli. — The following passages, of 

 which a literal translation is subjoined, occur in Borelli's Treatise on 

 the Telescope and other magnifying glasses, viz. De vero Telescopii 

 inventore cum brevi omnium Conspiciliorum Historia. Autliore Petro 

 Borello. Hagse-Comitum, 1655. The copy of this work in our library 

 is in fair condition, though two pages, including the portrait of the 

 author, are wanting. 



Book i. p. 10 : — " And lastly the Microscope, or the fly or flea spy- 

 glass, by which the flea and the fly rise to (the size of) the camel and the 

 elephant, is made of two glasses inclosed in a tube ; the glass nearest 



