172 ANNUAL OF SCIENTIFIC DISCOVERY. 



and therefore are not so well suited as small ones for the purposes of sub- 

 marine transmission of telegraphic signals ; and 



That by the use of comparatively small coated wires, and of electro-mag- 

 netic induction-coils for the exciting agents, telegraphic signals can be trans- 

 mitted through two thousand miles with a speed amply sufficient for all 

 commercial and economical purposes. 



ON THE DEPOSITION OF THE ATLANTIC TELEGRAPH CABLE. 



In a discussion which took place at the last meeting of the British Asso- 

 ciation, on the deposition of the Atlantic Telegraph Cable, and its arrange- 

 ment upon the bottom, it seemed to be universally admitted that it was 

 mathematically impossible, unless the speed of the vessel from which the 

 cable was payed out could be almost infinitely increased, to lay out a cable 

 in deep waters (say two miles or more) in such a way as not to require a 

 length much greater than that of the actual distance, as from the inclined 

 direction of the yet sinking part of the cable, the successive portions payed 

 out must, when they reached the bottom, arrange themselves in wavy folds ; 

 since the actual length is greater than the entire horizontal distance. The 

 fact, therefore, which, when noticed, led to the increasing of the strain on 

 the Atlantic cable until it broke ought to have been anticipated, and must 

 be provided for in the future progress of that great national undertaking. 



GEAHAM'S IMPROVED MAGNETIC COMPASS. 



In this recently patented compass, by Capt. Graham, of England, the 

 local attraction in iron vessels is counteracted by means of a series of per- 

 manent magnets. Instead of being laid down on the deck as in the old 

 plan of adjustment, these magnets, four or five in number, are disposed on 

 a frame round the compass and on a level with the card, and are so arranged 

 as to bring their polarities into correlative lines. Each magnet is fitted with 

 a screw, by which it may be brought nearer to or drawn back from the com- 

 pass by simply turning a small key. The effect of these magnets is to sur- 

 round the compass with a well balanced and tensible force which cuts off or 

 neutralizes all local derangements. Whatever the amount of disturbance 

 may be, the magnets can be so brought to bear upon the compass as to over- 

 come it. Great steadiness is thus imparted to the needle, preserved as it is 

 from oscillation by invisible threads of influence issuing from the magnets, 

 while at the same time what is called " the sluggishness " of the needle is 

 dissipated, its energy and sensitiveness are increased, or in other words it is 

 rendered more susceptible of influence by the natural magnetic current, and 

 consequently a more prompt and truthful indicator of any alteration in the 

 ship's course. 



IMPROVEMENTS IN THE ELECTROTYPE PROCESS. 



At the Dublin meeting of the British Association M. L'Abbe Moigno 

 read a very interesting paper " On three new Electrotype Processes," and 



