Monthly Mi ical . 5 
Sipe tr pearay a and their Merits. 285 
friction rollers, an invention of Tolles, and which he (Hagen) had 
seen various modifications of on several of Tolles’ instruments, in 
particular the first one in which it was ever introduced; yet he 
failed to notice it there. 
It may, perhaps, be urged for Dr. Hagen that these things are 
trivial, and to some they may look so; but they constitute Dr. 
Hagen’s paper; the aggregate of the trivialities makes about the 
whole. Dr. Hagen fails throughout all his papers to appreciate 
the difference between magnifying power and quality. 
With a patronizing air that is “ nearly comical,” after reading 
the paper, he compliments the artists in these words :—“ Messrs. 
Tolles and Wales are no doubt artists of the first water, constantly 
endeavouring to advance and enlarge their science.” 
Dr. Hagen admits that he has not exhausted his subject, and 
promises to renew it; it is to be hoped that he will, and that when 
he does he will spare no pains to make himself thoroughly ac- 
quainted with it; if he endeavours to do that, all our microscopists 
will cheerfully assist him.— American Naturalist, vol. iv., No. 7. 
