12 THE UNIVERSE. 



not enter his work-room; a mechanism, moved by clock- 

 work, at a s^^itable hour sets the machine in movement; 

 the invisible divisions of the glass-plate are engraved by 

 means of an excessively fine diamond spark, which is 

 fomid to be totally worn out when its Avork is accomplished. 



But the means of investigation at the disposal of the 

 microscopist do not end here. In observations of extreme 

 dehcacy micrometers are called into requisition which 

 are almost marvels, being constructed with an ingenious 

 mechanism capable of dividing a milhmetre into 10,000 

 parts by moving spiders' threads with the aid of a simple 

 screw. He also utilizes in a thousand ways both simple 

 and polarized light, as well as chemical re-agents; and as 

 these last, owing to the vapours they disengage, injure 

 the glasses and make them dull, those who work with 

 the microscope, in order to avoid the inconvenience thus 

 occasioned, employ particular instruments, the lenses of 

 which are placed below the objects to be magnified. 



After this demonstration of the resources at its com- 

 mand, will any one accuse micrography of giving rise to 

 those vain illusions with which those Avho do not enter 

 upon the investigation it requires with a proper degree 

 of patience, are pleased to reproach it? Perchance! for 

 this science has never ceased to recall the interminable 

 discussions which overhung its cradle. The dispute be- 

 tween Leuwenhoeck and Hartzoeker is not yet allayed. 



