66 On the Oay-calciwm Light. — [Mouth Awe tera 
fixed point nothing would be left to desire.” Dr. Beale* tells us 
that some of the pictures of these gentlemen were remarkably good, 
“they possess a peculiar delicacy in the half tones and the shadows, 
with much roundness of the objects, but the definition, as might be 
expected, does not quite equal in some of the finest markings prints 
obtained from sun negatives.” A perusal of Dr. Wilson’s paper 
will show that my process differs from his in the use of the following 
precautions: the interpolation of an ammonio-sulphate cell to ex- 
clude the non-actinic rays, the use of lenses specially made for photo- 
graphy for all powers from the 3th down, the use of much larger 
condensers to concentrate the light, and so to shorten the exposure, 
and in the case of the Magnesium light, in the use of a clock-work 
lamp to increase the steadiness of the illumination. ach of these 
points are in my judgment essential to obtain the best results. 
I learn from the same letter of Dr. Maddox that he had himself 
made experiments with the Magnesium lamp some time before those 
of Abercrombie and Wilson. He used powers as high as a fifth, and 
appears to have obtained better results than I supposed anyone 
had done prior to the publication of my Report. He gives me the 
following account of his experience :—“The first picture I took 
with the Magnesium light was done in a very rude way. An inch 
and a quarter of wire was held in a small spirit flame and advanced 
by hand as burnt. The objective was Beck’s 2rds, the object the 
sycamore-leaf insect, and about 2ths of an inch of wire remained 
after use. I sent a print, with a sun print of the same, to the 
‘ British Journal of Photography,’ and in the number for July 1, 1864, 
you will find some remarks by myself and the editors. Now to 
try and meet any error that might arise from what we may term 
want of correction, I used the 2rds with the correcting lens, which 
is excellent for sunlight; the picture was soft, full of half tone, but 
wanted, as in other pictures I have seen by artificial light, the 
decision of definition in the outlines.” “ After this I used the 1th 
with the little apparatus sketched in Beale’s book,f and which, I 
venture to think, embraces all that is required for its use, provided 
the condenser has its focus at the burning point, and that the 
reflector has the same.” ‘ With the 1th, fibres of cotton and mus- 
cular fibrille of boiled shrimp, with several other objects, were 
taken, but I did not use any higher power, nor indeed pay much 
attention to the subject, as I gave the preference to the sun-lighted 
prints and negatives.” I give these extracts with great pleasure, 
as showing the experience in this direction of one of the most dis- 
tinguished labourers in the field of Photo-micrography, and regret 
that I was not acquainted with them at the time of publishing my 
first Report. The method of Dr. Maddox, however, differed from 
mine in the same essential points as that of Abercrombie and Wilson ; 
* “How to Work with the Microscope,’ 4th edition, p. 248. + Page 275. 
