THE APRIL MEETING, 1844. 441 



long since, Wheatston of England, aided by ouf own great mechanic, Saxton 

 solved the problem. This has induced Arago, of France, to propose to test the rival 

 theories of light, by similar means — to measure thus a velocity, to detect which has 

 heretofore required a motion over the line of the diameter 'of the earth's orbit. 



In galvanism, our countrymen have made many important discoveries. Dr. 

 Hare invented instruments of such great power as well to deserve the names of 

 calorimeter and defiagrator. The most refractory substances )-ielded to the action 

 of the defiagrator, melting like wax before a common fire. Even charcoal was 

 supposed to be fused in the experiments of Hare and Silliman, and the visionary 

 speculated on the possibility of black as well as white diamonds. Draper, by hia 

 most ingenious galvanic battery, of two metals and two liquids, with one set of 

 elements, in a glass tube not the size of the little finger, was able to decompose 

 water. Farraday, of England, discovered the principle, that when a current of 

 electricity is set in motion, or stopped in a conductor, a neighboring conductor 

 has a current produced in the opposite direction. Henry proved that this prin- 

 ciple might be made available to produce an action of a current upon itself, by 

 forming a conductor in the whirls of a spiral, so that sparks and shocks might be 

 obtained by the use of such spirals, when connected with a pair of galvanic plates, 

 a current from which could give no sparks and no shocks. Henry's discoveries of 

 the effects of a current in producing several alternations in currents in neighbor- 

 ing conductors, — the change of the quality of electricity which gives shocks to the 

 muscles into that producing heat, and vice versa, — his mode of graduating these 

 shocks, — his theoretical investigations into the causes of these alterations, — are 

 abstruse, but admirable ; and his papers have been republished throughout Eu. 

 rope. The heating efi'ects of a galvanic current have been applied by Dr. Hare 

 to blasting. The accidents which so often happen in quarries may be avoided 

 by firing the charge from a distance, as the current which beats the wire, pass- 

 ing through the charge, may be conveyed, without perceptible diminution, through 

 long distances. A feeble attempt to attribute this important invention of Dr. Hare 

 to Col. Pasley, an English engineer, has been abandoned. This is the marvellous 

 agent by which our eminent countryman, Morse, encouraged by an appropriation 

 made by Congress, will, by means of his electric telegraph, soon communicate in- 

 formation forty miles, from Washington to Baltimore, more rapidly than by whis- 

 pering in the ear of a friend sitting near us. A telegraph on a new plan at that 

 time, invented by Mr. Grout, of Massachusetts, in 1799, asked a question and re- 

 ceived an answer in less than ten minutes through a distance of ninety miles. 

 The telegraph of Mr. Morse will prove, I think, superior to all others ; and the day 

 is not distant when, by its aid, we may perhaps ask questions and receive replies 

 across our continent, from ocean to ocean, thus uniting with steam in enlarging 

 the limits over which our republic may be safely extended. 



Many of our countrymen have contributed to the branch which regards the ac- 

 tion of electrified and magnetic bodies. Lukens' application of magnetism tosteel, 

 (called touching,) the compass of Bissel for detecting local attraction, of Burt for 

 determining the variation of the compass, and the observations on the variations 

 of the nocdlo made by Winthrop and Dowitt, deserve notice and commendation. 

 Not long since. Gauss, of Germany, invented instruments, by which tho changes 

 of magnetic variation and force could bo accurately determined. Magnetic action 

 is ever varying. Tho needle does not point in the same direction for oven a few 

 minutes together. Tho force of magnetism, also, perpetually varies. True as ths 



