% Wen HAM, on Microscopic Photography, 
ance, others will probably be better able to judge than myself. 
I have not worked at it with sufficient diligence to make a 
choice selection, but have taken them as they came. I should 
judge that the whole of them, to the number of twenty-two, 
had occupied about six hours of sunlight, of course including 
some failures. 
If the photographs are intended for illustration, it is re- 
quisite that they should each be included in a given space. 
The position of the sensitive surface must in consequence be 
made to vary, more or less, for every different object, accord- 
ing to its size. A range of from five to ten feet is oftentimes 
required. A box of this length is both inconvenient and 
cumbrous, and it is a matter of some difficulty to get access to 
the furthest end for the purpose of focussing the object accu- 
rately. For these and other reasons, I have altogether aban- 
doned the use of the microscope camera, and given the 
preference to the method herein described. 
In the first place, it may be proper to offer a few remarks 
on the subject of the illuminating source, as I have tried many 
experiments with the view of obtaining an artificial light suit- 
able for photographic purposes. A light may appear strongly 
luminous, and yet possess but a feeble degree of photographic 
intensity ; and I have not yet succeeded in producing a satisfac- 
tory result from either gas, oil, or camphine lamps. Burning 
phosphorus will give a more rapid impression, but its use is 
both inconvenient and expensive. Fine zinc turnings, burnt in 
atmospheric air, equal or surpass this ; a ball of about three- 
quarters of an inch in diameter will last a sufficient time to 
give a distinct impression. As it is of no consequence whether 
the light is intermittent or not, I have produced an image 
from a succession of electric sparks, arising from the spon- 
taneous discharge of a small Ley den jar, containing about thirty 
inches of coated surface, the discharging knobs being placed 
in the axis of the lenses for condensing the light upon the 
object. The electric spark contains a large proportion of the 
actinic rays ; I found that about one hundred discharges pro- 
duced a good impression. The electric light between charcoal 
points I have not yet tried. In a few instances I have used 
the hydro-oxygen, or lime light, but I consider that it does 
not possess that degree of actinic intensity which its brilliancy 
and appearance would seem to indicate. 
It has been proved that the two latter may be successfully 
applied for obtaining photographic impressions, but they are 
both troublesome and too much out of the way of the micro- 
scopist to be generally useful. 
I have merely mentioned these experiments with the view 
