Intelligence and Miscellaneous Articles. 75 



Thanks to the kind assistance of Dr. J. Barrois, director of the 

 zoological station of Villefranche-sur-mer, the ' Albatros,' despatch 

 boat of the French Navy, was placed at our disposal for several 

 days. The intelligent and ready cooperation of the lieutenant of 

 the ' Aboiville/ the commander of this vessel, and of all the officers, 

 greatly contributed to the success of these delicate experiments. 



Our mode of proceeding was the same as in the experiments on the 

 Lake. A Monckhoven gelatinobromide-of -silver plate was immersed 

 to a given depth, in the apparatus, which remained open during a 

 fixed time. On this occasion we were obliged to preserve the 

 sensitive layer from the chemical action of the sea-water by covering 

 it with a thick coating of varnish. The light acted from the back 

 of the plate and through the thickness of the glass. Repeated 

 washings with spirits of turpentine and absolute alcohol sufficed to 

 remove the varnish before proceeding to develop. As on the former 

 occasion, we employed oxalate of iron as the developing agent, 

 which in every case was allowed to act for ten minutes. 



The experiments were made on the 25th and 26th of last March, 

 and were favoured by bright and calm weather. We found the 

 depths we wanted, that is to say from 400 to 600 metres, off Cape 

 Ferrat, which protects the entrance to the Bay of Villefranche, 

 Leaving unnoticed the plates of minor interest, we will quote the 

 following, which appeared to us sufficient to solve the question. 



a. Between lOh 30rn and lOh 40m a plate exposed at a depth of 200 



metres to begin with ; the boat drifting away from the shore we 

 were obliged to let out 60 metres more rope in order to prevent 

 the premature closing of the apparatus. 



b. From 12.45 to 12 50 at a depth of 280 m. 



c. Between 11.30 and 11.40 at a depth of from 345 to 350 m. 



d. Between 10.55 and 11.5 at a depth of 360 m. 



e. From 10.15 to 10.25 at a depth of 380 m. 



This experiment was made under especially favourable circum- 

 stances ; there was neither wind nor swell, the boat remained 

 absolutely motionless, the line perfectly vertical, so that we were 

 not obliged to let out the line throughout the time of exposure. 

 /. From 1.20 to 1.30, under a cloudy sky, but still luminous enough, 

 at a depth of 405 to 420 m. 

 All these plates, with the exception of plate/, were exposed while 

 the sun was shining brightly. 



On developing, the plates a and b proved to be greatly over- 

 exposed. On the plates c, d, and e, the strength of the impression 

 went on diminishing in a ratio corresponding very regularly with the 

 increase of depth. On the plate e the strength of the impression 

 was notably inferior to that produced by an exposure during the 

 same length of time to the air on a clear night with no moon. It 

 is comparable to that produced by an exposure of half the time, 

 say of five minutes only, under these latter conditions. 



Lastly, the plate /did not bear the least trace of any impression 

 whatever. It is no doubt to be regretted that this last experiment 

 did not take place, like the others, under a perfectly clear sky. 

 But the impression on plate e % at 380 m., was already so faint that 



