42 KNIGHT — ON OYSTER CULTURE. 



to be that atomic ' ' magnetic " power in the battery which produ- 

 ces magnets at the will of the operator, by his voluntary me- 

 chanical agency ; and that mugnetism is the primary power and 

 action through which the line operates. Electricity being merely 

 a conditional effect of the polar reciprocal action of the magnets, 

 both poles being positive, under different conditions, and not 

 one positive and the other negative, as is generally supposed, 

 all that is required of a telegraph line is that its wire be 

 *' solid" in length, and thoroughly insulated from the moist 

 earth, as the present Atlantic cables appear to be. Yet a tele- 

 graph cable that will gradually lose the iron may thus be of less 

 weight and dimensions where the water deepens, and can still 

 have these two properties ; it would thus avoid all the difficul- 

 ties met with in the frequent attempts to lay the Atlantic cables, 

 that were finally surmounted by strictly mechanica} Jofpce, in 

 preference to their being avoided by an examination of the 

 natural law and force of the material, and applying that law 

 to those lines before attempting to lay them. The operation of 

 which law on such material, I am now prepared to illustrate and 

 explain to you by experiment, for your observation. 



Art. V. Oyster Culture in France. By T. F. Knight. 



(Eead February- 3, 1868.J 



In the application of science to industry France has long 

 afforded a distinguished example, partly through the scientific 

 geniua of the natipn, and partly through the encouragement 

 which is given to scientific progress by the French government ; 

 and in no branch of scientific industry has she more excelled 

 than in the art of Pisciculture. In France, it is well known, 

 the first successful experiments were made to revive the ancient 

 practice of breeding fish from the ova taken from the living 

 animal ; so that by a process of cultivation, from small begin- 

 nings, so greatly did the art of artificial propagation succeed, that 

 valuable fisheries that had declined, were restored to fertility, 

 and new localities were stocked with young, that soon teemed 

 with the fruits of natural increase. 



