THE LIGHT. 37 
poses ; but to employ an electric light for this object 
alone would involve an expense which few would 
care to incur. The same may be said of the mag- 
nesium and of the calcium lights. Dr. Woodward 
some years since demonstrated that all these 
lights may be used, but the result of his experi- 
ments was that sunlight is preferable, indepen- 
dently of the question of expense. 
Photo-micrographs may also be made with a 
powerful oil-light, and for low powers this source 
of illumination should probably be placed next 
to sunlight for convenience and cheapness. The 
writer made some experiments a year and a half 
ago which satisfied him of the practicability of 
making good photo-micrographs in this way, and 
also of the superiority of sunlight. 
Recently, Professor C. Henry Kain has obtained 
some very creditable results with an ordinary 
kerosene lamp and an amateur photographic out- 
fit. The editor of the journal in which Profes- 
sor Kain recorded his results has also met with 
success in photographing by lamplight, and has 
written an interesting article upon the subject.’ 
Black-ground Illumination. 
Black-ground illumination is effected by stop- 
ping out the light immediately behind the object 
by means of an opaque cement applied to the 
central portion of the front lens of the condenser. 
1 See the Amer. Month. Micr. Journal, Vol. III. No. 4, p. 71. 
2 Ibid., Vol. III. No. 5, pp. 88-92. 
