1895.] MICROSCOPICAL JOURNAL. 89 



In order to guard against ordinary errors of spherical 

 aberration in making the drawings, Mr. Tolman con- 

 structed a movable platform with double rectiliniar 

 motion on which the microscope traveled across the table, 

 as it was impossible to get more than a small portion of 

 the attestation clause in the field of the microscope at 

 one time. Besides the drawings before described there 

 was a camera lucida copy of the signature and photo- 

 graphs of a number of checks, letters, etc. 



A Convex Illuminator. 



BY PROF. WILLIAM lylGHTON, 



OMAHA, NEBRASKA. 



During the past year I have examined and tested 

 several homogeneous immersion objectives for friends, 

 using Amphipleura pellucida, mounted in balsam, styrax. 

 Smith's medium and dry, and during these experiments 

 I have used a little piece of apparatus which I invented 

 some time ago, with such comfort and success that I 

 really think a description of it may be of interest and 

 help to microscopists using high power homogeneous 

 immersion objectives. I have found, in quite an ex- 

 tensive series of experiments that many objectives fail 

 to do their best when using oblique light, because of 

 the use of too large lamp-flame, coupled with too great 

 diameter to the concave mirror. Now, a small flame 

 does not give sufficient illumination without the use of a 

 condensing lens of considerable diameter, and that is 

 quite as bad. The plan now proposed is to use sunlight 

 in the manner to be described, and the apparatus need 

 not cost more than a dollar or two, and it can be used 

 for either visual work or photography. 



A plano-convex lens of about four inches diameter and 

 six inches focus is obtained and the plane side is painted 

 black with paint that will not crack. The object of this 

 paint is to destroy the internal reflection from the plane 



