441 
THE APRIL MEETING, 1844 . 
long since, Wheatston of England, aided by our 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 lof 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 deflagrator. The most refractory substances yielded to the action, 
of the deflagrator, 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 his 
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 abie 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 effects 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 heats 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 to steel, 
(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 needle made by Winthrop and Dewitt, deserve notice and commendation. 
Not long since, Gauss, of Germany, invented instruments, by which the changes 
of magnetic variation and force could be accurately determined. Magnetic action 
is ever varying. The needle does not point in the same direction for even a few 
minutes together. The force of magnetism, also, perpetually varies. True as the 
