352 Chronicles of Science. [ April, 
was confirmed by experiment, and by the application of heat alone 
the indifferent yellow iodide of silver becomes.so changed in its pro- 
perties, as afterwards to darken on exposure to sunshine much in the 
same way as the ordinary modification of bromide of silver. Very 
little apparent change is produced by the action of heat; at the most, 
the iodide can be said only to lose in a trifling degree the brilliancy 
of its yellow colour, verging a little towards grey. The lowest limit 
of temperature at which this change takes place is 350° Fahr.; and 
if the heat be augumented to 400° and upwards, the change is more 
rapidly effected. On increasing the heat, the iodide fuses to a dark- 
red fluid, which cools to a pale yellow semi-transparent mass, quickly 
affected by exposure to light. 
Photographers are gradually recognizing the truth of what Sir 
William Newton urged more than ten years ago, namely, that it is 
possible to have pictures too sharp, and that the most artistic por- 
traits were frequently those which were not absolutely in focus. One 
of our first writers on Art Photography has lately urged, in the ‘ British 
Journal of Photography,’ the beauty of effect arising from slight want of 
sharpness. What artists call “ hardness,” is generally that effect which 
photographers call “sharpness ;” and he maintains that far more pleasing 
portraits would be obtained were photographers to use their “long, 
long pencils of light much as artists use their drawing pencils,—that 
is to say, with a somewhat broad instead of an extremely sharp point.” 
Although to an ardent photographer such doctrines may savour of 
rank heresy, we honestly confess that we have seen far more pleasing 
portraits taken in accordance with this artistic theory than when they 
were focussed with microscopic accuracy. 
A writer in ‘La Lumicre’ proposes a novel lantern for evolving 
light sufficient for taking portraits at night. A furnace is constructed, 
fed with hard retort carbon, and supplied, not with air alone, but with 
a mixture of oxygen and air: the oxygen being evolved from a mix- 
ture of binoxide of manganese and chlorate of potash, contained in a 
cast iron bottle placed beneath the furnace. In a small furnace 
furnished with a good draught, and only supplied with air, a light 
was obtained equal to 100 candles, and the author thinks that if fed 
with oxygen, the light would be equivalent to 1,000 candles. We do 
not glean from his description that such an experiment has been 
actually made, and we are tolerably confident that the difficulties in 
its practical accomplishment would prove too great to supersede other 
sources of artificial light, which have been recently introduced. 
The Electric light has always been a favourite amongst advocates 
of night photography. At a recent meeting of the American Photo- 
graphic Society, Mr. J. A. Whipple, of Boston, exhibited some photo- 
eraphs of a fountain in Boston Common, taken at about ten o’clock in 
the evening, whilst illuminated with the electric light. The exposure 
was 90 seconds, and from a comparison of the effect produced when 
photographed in daylight, it was estimated that the intensity of the 
electric light as compared with that of weak sunlight, was in the pro- 
