1892.] 



THE MICROSCOPE. 



141 



WAYS 



AND MEANS 



Camera Obscura.— ^Nlr. Hans M. Wilder, of Philadelphia, 

 calls attention to an item m Joiu-nal oi the British Dental Asso- 

 ciation for February, bearing upon our two articles in March 

 number, as follows : 



A. Hopewell Smith uses the concave mirror for that purpose. 

 Place the microscope horizontally, as usual, and remove the 

 mirror from its attachment. The slide having been put upon the 

 stage, condense the lamplight upon it by means of a bull's-eve, 

 taking care to centre the light. The concave mirror is then "at- 

 tached to the front of the eye-piece in some fashion, so as to form 

 an angle of about 45° with the plane of the eye-lens. The image 

 will now be found projected onto the paper, and no distortion 

 will occur if the outer ring of the light \% perfectly circular. A 

 dark cloth is thrown (photographer-fashion) over the head and 

 body of the microscope, in order to exclude the light. This ar- 

 rangement can be used easily with amplifications up to ^00-600 

 diameters. 



It will be remembered that Dr. Jos. Collins (p. 77) and Dr. 

 H. G. Piftard (p. 3) both desire to exclude extraneous light. 

 Mr. Wilder thinks it advantageous to use the black cloth thrown 

 over the head after the manner of photographers. Pin or fold it 

 together around the tube of the microscope. 



C°RRESP°NDEnCC 



^^ 



mmm^^m^m 



lC>l,&4.&oJU^ 



Barbadoes Earth. — Referring to query No. 16, Rev. F. B. 

 Carter writes : 



" Barbadoes earth may be had of S. S. Day, Prudential Build- 

 ing, Newark, N. J. It is from the Springfield estate. I know 



