1892.] THE MICKOSCOPE. 135 



about four inches, and when one of the frames was turned so that 

 the glass space was at a different angle to the others, the thread 

 was seen to pass through the same variations which, under simi- 

 lar conditions, a beam of light would be forced to pass. 



EDITOFiS 



^^ DEPARTMENT 



Demand for Cheap Apparatus. — We are constantly pub- 

 lishing descriptions of home-made articles because some micro- 

 scopists invent them and others want to imitate them. It is not 

 a little surprising when a doctor writes that, not having the money 

 to spend for a microtome, he had made one with a few cheap 

 materials. But such incidents are of common occurrence. We 

 know men who buy things on installments for use in microscopy. 

 Devotion to science in such circumstances is little short of hero- 

 ism, and we shall foster it by publishing every little device we 

 can hear of, except when the inventor patents it, or when he 

 sends the description of it to some obscure periodical which hojDCS 

 to get out of its obscurity by copyrighting the description. In 

 that case our readers will know why we do not report the device. 

 We appeal, however, to every one who devises some little thing 

 of general utility, to insist that other people's patents and copy- 

 rights be kept off of it, and that its use be open to the entire mi- 

 croscopical world without money and without price. 



Resolving Amphipleura. — A gentleman wdio does not wish 

 to posture as a critic but who wants to understand the matter 

 writes in reference to "Amateur's" article in the ]March number, 

 p. 94. 



Amateur claimed to have veso\yedA??ip/nple2ij-a into transverse 

 striie with a dry -^ objective and 2-inch eye-piece. To this, in- 

 quirer says : " The unaided human eye can separate no more than 

 250 lines to the inch (Abbe), The stride are over 90,000 to the 

 inch. Dividing 90,000 by 250 gives 360 as the number of diame- 

 ters which the microscope must magnify in order to show the 

 stride. A 4 lens with 2-in. ocular magnifies onlv 250 times. Will 

 you arrange your apparatus as you had it in resolving A. pellucida 



