THE LIGHT. 85 
The writer would repeat the advice already 
given to those who propose to learn to make 
photo-micrographs, to commence with the simplest 
apparatus, and not to purchase a heliostat and 
accessories until a certain amount of practice has 
demonstrated the aptitude of the student for mas- 
tering technical difficulties, and his continued 
desire to photograph more difficult objects with 
higher powers. 
Those who desire to purchase are recommended 
to buy the heliostat manufactured by Edward 
Kiibel, of Washington, D. C. (No. 328 First Street, 
N.E.). This instrument, with the accessories, first 
made under the direction of Surgeon J. J. Wood- 
ward, United States Army, is especially adapted 
for the purpose, and it is doubtful whether a 
cheaper instrument, if one is made, would prove 
as satisfactory. 
The price given by Mr. Ktibel about a year ago 
is as follows : — 
Keith’s heliostat with extra size mirror . . . $54.00 
Woodward governor . . 2 oe ew ee ~~ 86.00 
Mounted actinic eget lens » © « « » 10.50 
Bluecell . . . . a ae 4.00 
Blue cell holder and six Aiaphesgas ae; snes 7.00 
Foot-plate for heliostat. . . . 2. . 2. .. 1.75 
In northern latitudes, and during the winter 
months, the sun is so low in the heavens that the 
mirror of the heliostat, being greatly inclined, 
gives only a narrow line of light. For this reason, 
and because of the diminished actinic power of 
the light, those who live in southern latitudes 
