334 
POPULAR SCIENCE REVIEW. 
PHOTOGEAPHY. 
Fhotographmg the Eclipse. — Next montli will be signalised by a total 
eclipse of the sun, of almost the greatest possible duration. Astronomers 
are looking forward to this with considerable interest in connection with 
arrangements taken for photographing it. Major Tennant, of the Great 
Trigonometrical Survey, assisted by Captain Brandreth and three non-com- 
missioned officers of the Royal Engineers, passed some time with Mr. 
Warren de la Rue, at his observatory at Cranford, practising to perfect 
themselves in Astronomical Photography before their departm*e for India. 
The expedition, originated by the Astronomical Society, will use a telescope 
constructed for the occasion by Mr. Browning, F.R.A.S. It is a reflecting 
telescope of the Newtonian form, by which the image is thrown out at the 
side of the tube, and is furnished vrith a mirror of silvered glass 5 ft. 9 in. in 
focus, and closely resembles that used by Mr. De la Rue. This instrument, 
set up at Guntoor or Masulipatam, will concentrate the light to an enormous 
extent, and as no attempt to magnify the image by interposing lenses be- 
tween the mirror and the plate will be used, great rapidity may be expected 
in the exposing of the plate. It is calculated, as the totality will last nearly 
five minutes, not less than six negatives will be obtained in that time. 
Micrometic wires and other devices will be adopted to secure accurate 
register when putting the plates in position, and extraordinary care used to 
guard against possible chemical defects. The collodion, iodised with iodide 
of cadmium only, on the recommendation of Mr. De la Rue, wiU be sensi- 
tised in a bath of 30 or 35 grns. of silver to the ounce, developed with aceto- 
pyrogallic acid, and the image fixed with hyposulphite of soda. 
Keeping the Silver Bath in good order. — Mr. 0. G. Reylander, to achieve 
this desirable end, keeps his sensitising baths, when not in use, in the lights 
instead, as is usual, in the dark, and gives as a reason for adoptiug the plan,, 
that any injurious matter contained in the solution may be at once detected 
by the reducing action of the light, when its removal by filtration can follow 
as a prompt and easy remedy. 
Photographing Coast Scenery. — Photographs of this description can fre- 
quently only be obtained from a boat. To render this possible, M. Kruger 
has adopted the following plan. He has a tripod stand for his camera 
thirty feet in length. To this iron weights are attached by stout chains, so 
that, when it is planted in the water at a sufficient distance from the 
shore, the waves do not in any way disturb it, and a plate prepared in the 
boat under a dark tent, can be exposed with ease and without being shaken. 
In this way some excellent photographs have been taken, such as could not 
otherwise have been procured. 
Filtering Bath Solutionis. — Mr. A. Brothers, F.R.A.S., points out, in the 
Illustrated Photographer, a hitherto unsuspected source of contamination to 
the silver bath, arising from the use of white filtering paper, containing, 
probably, hyposulphite of soda. From what we have since heard on the 
same subject from various experienced photographers, we conclude that 
white filtering paper is one of those things which operators should avoid. 
It is said, upon tolerably good authority, that no white English-made 
