n6 Progress in Physics. [January, 



plates, being 4 inches by ij, decompose water very energetically. The metal 

 aluminium possesses the advantage of costing (for equal surfaces) about one- 

 tenth the price of platinum, being about 5s. per ounce, cut to size. 



The subject of the electro-deposition of brass is one of some commercial 

 importance; it has been recently studied with considerable success by Mr. W. 

 H. Walenn. The history of electro-metallurgy, as set forth by Smee, in 185 1, 

 comprises only that part of the subject which relates to the electro-deposition 

 of metals from their neutral or acid solutions. With some isolated exceptions, 

 no alkaline solution is there treated of. Mr. Walenn uses potassic cyanide 

 and neutral ammonium tartrate, when mixed with water, to form the solvent 

 solution for brass. The quality of brass (yellow or red) depends upon the 

 heat of the solution. Acid solutions, in general, give a spreading, or matted 

 deposit ; alkaline solutions, a bristling one. The contact of the coating is 

 promoted by working the solution hot. The article should be pickled, scrubbed 

 with sand, washed, scrubbed with a portion of the depositing solution, and 

 then placed in the depositing trough ; after deposition the article is washed, 

 and dried in hot mahogany sawdust. Complete protection from rust, and a 

 satisfactory coating for any purpose, is given by the use of an acid-depositing 

 bath subsequent to that of the alkaline bath. 



The self-recording instruments at the Kew Observatory, showed a large 

 amount of disturbance of the magnetic declination and horizontal force during 

 the progress of the Aurora of the 25th of October. Dr. Joule also observed the 

 changes which took place in the magnetic dip, at Broughton, near Manchester. 

 The most remarkable variation occurred during the interval from 6h. 15m. to 

 6h. 23m. G.M.T., when the dip increased from 69 8' to 70 30'. 



Apropos to a statement which appears to be authentic, that there has been 

 in Versailles during the investment of Paris a telegraphist who has secretly 

 rendered most important services to his country, by transmitting information 

 from the head-quarters of the German army to the imprisoned authorities in 

 Paris, the " Electric Telegraph Review" enters into some interesting specu- 

 lations on the subject of secret telegraphy. It is considered by most persons 

 impossible that telegraphic communication could be carried on between 

 Versailles and the besieged capital without being discovered ; for, they argue, 

 even if we could not hit upon the line wire, we should obtain speedy information 

 of the locality where it terminates, and where this ingenious individual manipu- 

 lates his instruments. Is a secret telegraphic circuit, hidden from all ordinary 

 means of search, and capable of being worked from one extremity without the 

 exhibition of batteries, signalling instruments, or even a contact key — nay 

 more, without any appearance of " line" and " earth " terminals, beyond the 

 resources of modern telegraphic ingenuity, to say nothing of modern electrical 

 science ? Our contemporary thinks not. It appears certain that the subject 

 of secret subterranean telegraphs is one which has from time to time received 

 some attention in France ; and it is one which, sooner or later, would probably 

 well repay a little investigation on the part of our own Government. The 

 data, even as at present understood, seems to be nearly, if not quite, sufficient 

 to realise the object in view. Employes in the secret service would need to be 

 trustworthy and thoroughly efficient telegraph clerks, trained to send signals 

 rapidly and accurately without a " key " — or with merely a common-place 

 latch-key, bringing into interrupted contact an innocent-looking bell-wire and 

 a harmless gas pipe. They would require also to be thoroughly conversant 

 with the art of converting the tongue into a delicate receiving instrument. 

 The lines must be buried deeply, and excavations for other purposes, such as 

 gas and water pipes, and sewers, should be utilised when possible. The 

 choice of the locality for one terminal is of importance ; an out-of-the-way 

 bedroom in a public building, or in premises adjoining it, is generally to be 

 preferred. The outward appearance of the terminal has been already hinted 

 at ; it may be a real bell wire, — the point where this is connected with an 

 insulated wire, led below the foundations of the building, being of coure care- 

 fully concealed. "Earth " of course can be obtained wherever there is a gas or 

 water pipe. Devices such as these are very simple ; but it does not seem to 



