308 Miscellaneous Intelligence. 
distance upon the surface of the screen. This it will be remembered is 
the effect of the unaided carbon-light sending its rays equally in all 
Dace from the luminous ceatre, and falls vastly short of the illumi- 
nating force of the cone of collected rays which was seen stretching 
like the tail of a comet from the surface of the great reflector. Judgin 
from some recent experiments on the power of such a reflector to aug- 
ment the intensity of the light emanating from its focus, there can be 
no doubt that, along the axes of the cone when brought to its narrowest 
limits, the illuminating force of the carbon light as displayed on the 
State edie could be rivalled only by that of several millions of candles. 
shining opts along the same line. 
ve described observations, a thick screen was necessary on 
account of the reat intensity of the lights to be antagonized. I ne 
hardly say that the different color of the two lights added much to the 
difficulty of the measurements. But, by marking in each case the 
extreme limits on either side, it was practicable to adjust the screen 
pretty severe to equality of illumination. 
only previous experiment of precisely the same kind which I can 
recall is vo of Bunsen, cited in the books, which was made with a 
of 48 elements. In this the photometric equivalent of the 
earbon light. et estimated at 572 candles, or nearly 12 candles to the 
cell. My observations show a power more than three times as great, or 
about 40 candles to the cell, a difference due no doubt largely to the 
more intensive battery at my disposal and the cumulative effect of its 
arrangement. I suspect too that the elements in Bunsen’s observa- 
tion were of inferior size, but on this point I am without definite. 
information. 
2. Vermilion Rock Salt Mine at Petite Anse, Louisiana.—One of the 
facts of noe interest brought to light by the Southern rebellion is 
the discovery of an important deposit of rock salt of remarkable purity. 
in the island of Petite Anse, in Vermillion Bay, on the Gulf coast of 
Louisiana. By the kindness of Mr. Geo. D. Colburn, a large specimen of 
this salt has reached us. Its analysis by Dr. J. L. Riddell, of New Or- 
leans, gives the following composition : Chlorid of sodium 98°88, sulphate 
of lime 0-76, chlorid of magnesium 0-23, chlorid of caleium 0°13, =100. 
This analysis, it will be seen, makes the Petite Anse salt almost aye 
rings had been known on the island from an early period, but 
no suspicion existed of there being rock salt near the surface until the 
late owner, Judge Avery, with the view to improve the flow of water 
from one of the saline springs, caused an excavation to be made, when, 
at the moderate depth of only fourteen or fifteen feet from the surface, 
the laborers struck the — ow —— rock salt, which they at first 
ined must be ice. It w nee seegnivadss soa promt * ineal- 
culable advantage to the Sailacane te 
wealth to the owner. The Island of Petite Aas (Littl Elo island, oO = 
named from its shape, is a body of very fertile land, su 
ae et, ome Sea Eve et 
