Intelligence and Miscellaneous Articles, 71 
slides of which are closed by the action of a pair of levers joined 
like scissors and drawn by a weight ; they separate by the action of 
an antagonistic spring, as soon as the weight of the lead in touching 
the bottom ceases to act on the levers. Knowing the depth, we 
can regulate the length of the line by which the weight is suspended 
to the apparatus, soas to have the photographic plate exposed in a 
horizontal position, at a given distance below the surface of the 
water. After a given exposure the apparatus is withdrawn, and 
rapidly closes under the action of the weight. The time of expo- 
sure was ten minutes inall cases. ‘The development was made with 
the normal oxalate-of-iron developer, which was caused to act uni- 
formly for ten minutes on each plate. They were all of the same 
lot, and therefore coated with the same emulsion*. 
The experiments were made in front of Evian, where the lake 
has over a large surface a depth of 315 metres. Dr. Marcet was 
kind enough to place at our disposal on two occasions his steam- 
yacht, the ‘ Heron.’ Professor Forel, of Morges, had the goodness 
not only to lend us his sounding-line, but also to accompany us, 
and help us with his advice and his experience. 
On the 16th of August, in calm weather and with a brilliant sun, we 
exposed :— 
1, At 237 metres deep two plates, one at half-past twelve and the other 
at seven minutes past one. 
2. At 113 metres a plate at twenty minutes after two. 
3. At 300 metres deep (15 metres from the bottom) a plate at forty- 
four minutes past two. 
On the 23rd of September, 1884, in cloudy, but fine weather, the clouds 
slight and rather luminous, light wind varying from east to north, we 
exposed :— 
4, At 147 metres a plate at 1 o’clock. 
By sy) 170 bs ys 26 minutes past 2. 
6, ,, 118 ” ” 3 ” 3. 
7% » 95 4 ” 34 ” . 
As a comparison, we exposed on the 15th of August at 10 p.m., ona 
clear night, but without moon :— 
8. A plate in the open air for ten minutes. 
2. Nata © ” five ,, 
On developing, it was found that the plate 5 (800 metres deep) had re- 
ceived no luminous impression whatever. The same was the case with 
plate 1. Plate 5 at 170 metres was slightly clouded, almost like plate 9, 
which was exposed at night for 5 minutes. Plate 4 at 147 metres had 
been slightly acted on, more so than the plate which had been exposed at 
night for ten minutes. Of the two plates at 113 metres, the plate 6 of the 
* Preliminary experiments in rather shallow water showed that the 
apparatus worked as well as could be desired, and that when closed it could 
be left in full sunlight without any light getting to the plate. During 
exposure the glass was uppermost and towards the light. On this side 
characters and numbers were traced in black varnish. The sharpness 
with which these signs were produced in white on the developed plate, 
the purity of the edges of the image, which, restricted by the separation 
of the covering plates, only extended to the middle of the sensitive 
layer, prove that light could not penetrate accidentally. 
