294 RAMBLES OF A NATURALIST. 



Drebbel* in 1619, was at first a kind of telescope six 

 feet in length, and sometimes from six to seven inches in 

 diameter. Although it was modified by different phy- 

 sicists, it remained until a comparatively recent date in 

 so imperfect a condition, that observers looked upon it 

 chiefly as a sort of experimental toy, and therefore con- 

 tented themselves with using a simple microscope. 



The greatest defect of the compound microscope was 

 that the images were confused, and their outlines marked 

 with coloured fringes. This defect depends upon the 

 very nature of light, and for a long time it appeared 

 impossible to correct it. However, the attentive study 

 of the human eye led to the discovery of means 

 for making magnifying glasses achromatic. In 1757^ 

 an English instrument maker, DoUond, constructed tele- 

 scopes which were perfectly achromatic. 



Hence it seemed the simplest thing to apply the same 

 process to the microscope, but the difficulty increases so 

 much with the smallness of the glasses, that DoUond 

 himself does not appear to have made the attempt, for 

 we find that his microscopes remained unchanged. 



confirmed him more and more in the ideas which he had already 

 entertained in relation to the movement of our globe, and from that 

 moment he maintained the system of Copernicus with a tenacity and 

 energy that drew upon him the rigours of the Inquisition. It is 

 well known that at the very moment in which, to escape from this 

 terrible tribunal he had abjured what were termed his errors, he 

 exclaimed in striking his foot on the ground, " and yet it moves." 

 Distinguished in physics no less than in astronomy, Galileo 

 discovered the laws of the pendulum and the weight of the 

 atmosphere, which his disciple Torricelli fully demonstrated by 

 inventing the barometer. 



* Drebbel was a celebrated alchemist, who was born in Holland, 

 and died in London in 1634. To him is attributed the invention of 

 the thermometer and the discovery of the means of producing a 

 bright and permanent scarlet dye. 



