SCIENTIFIC SUMMARY. 
553 
degrees of success or failure ; some specimens being too soluble and some 
insoluble. If an unnecessarily thick film of gelatine be used, the drying 
is retarded, and the tissue becomes less manageable in mounting ; if too thin 
there is a loss of power and half-tone. A loss of its setting properties will 
result from boiling the gelatine too long in its first preparation. It is 
desirable to ascertain the minimum quantity of bichromate that can be 
added without running the risk of insensitiveness arising from the use of 
too little. When the tissue is dry it should be excluded from the air, 
which hastens its spontaneous insolubility, especially if a large quantity of 
the bichromate be used, through excess of which the gelatine may become 
insoluble even before it is exposed to light. Mr. Cooper, at the meeting of 
the South London Photographic Society, referred to above, recommended 
three instead of four parts of water to one of gelatine, or, where the latter is 
of the softest kind, even two parts of water ; but said the quantity will have 
to be varied according to the hardness of the gelatine. He pointed out as 
one of the results attending the use of too thin a solution of gelatine, the 
fact of the pigment being apt to separate itself and run into eccentric 
forms upon the surface of the collodion, instead of giving a film of uniform 
colour. For mounting, previously to development, Mr. Cooper prepared two 
solutions — No. 1 containing six grains of pure india-rubber to the ounce 
of benzole, and No. 2 consisting of the same quantity of india-rubber with 
ten grains of damar, in one ounce of the same solvent. The paper was 
immersed in No. 1, and the tissue floated on No. 2, and when both were dry 
and placed in contact, pressure and gentle rubbing sufficed to produce 
perfect adherence. For the re-mounting, gelatine has been strongly re- 
commended. The collodion used should give a very transparent, but at 
the same time, thick strong film. It is advisable before applying the 
gelatine to the surface of the collodion to gently warm the plate, the flow 
of the solution may be aided with a glass rod, and care should be taken 
to get an even surface of uniform thickness ; the time required for the 
drying of this will be about twelve hours, but will of course vary with the 
temperature and the thickness of the film. The sensitiveness of the film 
is said to be increased within certain limits by keeping. It is dangerous to 
hurry the development by increasing the temperature of the water, although 
when one is anxiously waiting to see the results of early experiments there 
is great temptation to do so. 
Photo- Sculpture . — We no longer wonder at seeing our portraits painted 
to perfection in a few seconds by the operations of mere sun-light, because 
the fact is a familiar one, and although the idea of sculpture executed by 
the same agency is rather startling at first, it is in sober reality a far more 
simple and less wonderful thing. A process which will give any number 
of outlines of any number of surfaces at one and the same time, must, 
when all these outlines are re-combined, give again the relief from which 
they had their origin. Acting on this idea, M. Willeme invented the 
process of Photo-Sculpture, which has recently been carried out in Paris, 
and is now being introduced in London by Mr. Claudet. 
The studio in which the four-and-twenty photographs necessary for the 
process of Photo-Sculpture are obtained in Paris, is a circular one, having 
a large dome of glass. From the exact centre of this dome, immediately 
