PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 389 



etudded with islands, and the southern or Pura clear in its course and 

 about 35 miles in width. The Amazon delta is not, as miglit be supposed, 

 an unhealthy region of swamps. It consists mostly of a sandy soil with a 

 rocky substratum. The mean temperature of three years observation is 

 81 deg. Fah., which is lower than that of portions of the country further 

 from the ecpiator. Singularly enough a district extending from the west 

 end of Marajo, about 80 miles in length and in breadth, presents all the 

 characteristics of a true delta, being composed of mud and sediment, inter- 

 cepted by deep channels. This district, now 140 miles from the sea, was 

 doubtless at no very distant period the true delta, and the seaward portion 

 constituted a series of islands lying oil' the mouth of the river. 



Mr. Stetson said that the amount of solid matter carried down by the 

 Mississippi river has been estimated by taking the mean of a series of 

 observations, and he had found that it was equal to a discharge at the 

 mouth of four cart loads every second of time. .r 



New Method of Extracting Gold. 



Dr. C. Calvert read a paper before the Chemical Section of the British 

 Association, in M'hich he proposed to dispense with mercury in the extract- 

 ing of gold from auriferous rocks, as many other inventors before him have 

 proposed. The agent employed in his method is nascent chlorine gas, 

 evolved from a mixture of common salt and the binoxide of manganese 

 ground up with auriferous quartz, in the proportion of two or three per 

 cent. "When sulphuric acid is added the liberated chlorine will attack the 

 gold, and upon allowing water to percolate through the mass it would dis- 

 solve out all the gold, as well as the copper and silver, which could be pre- 

 cipitated in the metallic state. The process is said to yield good results, 

 even when working very poor quartz. 



Fog Horn. 



Mr. DaboU, the inventor of this instrument, "designed to give warning to 

 ships enveloped in fog, has received an order from the British Govern- 

 ment for one to be used at Dungeness. It will consist of two twenty- 

 four inch caloric engines, placed side by side on an iron bed plate, on 

 wln'ch are also two iron air tanks or receivers, into which will be condensed 

 the air for blowing. But one engine will be in use at a time, the other 

 being a reserve in case of accident. The trumpet is intended to revolve 

 half way around and back in about a minute, and blow its blasts as it 

 moves around. 



New Printing Process. 



An invention has just been patented in Paris by means of which printing 

 can be done without the employment of ink. The process consists in the 

 introduction between the paper and the type of a sheet of some fabric, on 

 wliich is deposited lampblack and glycerine. 



Spectrum of Comet II, 1864. 



Prof. Donati, of Florence, has furnished a sketch of the spectrum made 

 by this comet. It resembles that produced by metals, the black bands 

 being broader than the luminous. 



