The Microscope. 223 



ordered the copies of the standard to be made by the writer several 

 years ago. Owing to this omission, it is said that the copies are 3 

 in. too long, according to their measurements. The copies that I 

 ruled were made to be used by transmitted light. But I am informed 

 that the comparisons were made by illumination through the 

 objective. The image received by the latter illumination will be 

 longer than the one received when using transmitted light. There is 

 also a difference between plain and concave mirrors and day and 

 lamp light. The committee should have known that, or, knowing it, 

 should have stated the methods employed for comparing the meas- 

 urements. A.11 questions of scientific interest should be approached 

 with candor, and all sources of error should, so far as possible, be 

 eliminated. Had this been done in this instance, the source of error, 

 if error there was, might have been discovered to the satisfaction of 

 all parties. The animus of the report is, perhaps, best explained in 

 its concluding paragraph, which is as follows: " The members must 

 look to Prof. Rogers for copies," etc. Now, being that Prof. Rogers 

 was on the committee, why did he not make the copies in the first 



place ? 



CHAS. FASOLDT, Sr. 



Albany, N. Y., June 6th, 1888. 



W. F. E., N. Y. City. — The little objects to which you refer are 

 mucous (also called salivary) corpuscles. The little bodies " dancing 

 about with the greatest activity " are indulging in the so-called 

 Brownian or Bruonian movement. You can find full information on 

 the subject in any good text-book under head of Brownian Move- 

 ment. ... 



H. E. v., Boston, Mass. — The distance from the eye-lerfs to the 

 paper should be the same as from the eye-lens to micrometer on 

 stage. 



E. D., Sandusky, Ohio. — To permanently preserve uric acid 

 crystals : A drop containing a number of the crystals is placed on a 

 slide and protected from the dust, allowed to dry without heat; when 

 thoroughly dried, a drop of turpentine is added. When the turpen- 

 tine has nearly evaporated, mount in Canada balsam. 



