1835.] Scientific Intelligence. 465 



the gold leaves of the latter. To determine the nature of the elec- 

 tricity which has thus been separated is easily accomplished, by means 

 of a glass rod excited, or a substance covered with a resinous coating. 



Dr. Ritchie suggested that by a modification of the galvanometer, 

 base coin may be readily detected. A bad sixpence which he sub- 

 mitted to examination produced a very rapid deviation in the needle. 

 He is of opinion that jtfW °f copper mixed with silver might be 

 by this method appreciated. 



Dr. Ritchie endeavoured to afford an explanation of Dr. Faraday's 

 experiment, in which, the spark was elicited in a long wire, by the 

 consideration, that one particle of light does not communicate light. 

 Now, in the long wire the quantity of electricity was smaller than in 

 the short wire, but took a longer time to arrange itself. 



The able lecturer exhibited an electro-magnetic machine, in 

 which he had devised some improvements, by which combustion and 

 decomposition can be as readily effected and more conveniently than 

 with a voltaic pile. This affords an excellent instrument for class 

 room experiments. 



Dr. Lardner on Halley's Comet. 10th April. Up to the 

 time of Kepler, philosophers were in the habit of forming systems 

 and cutting down nature to suit their own theories. He produced, 

 however, a revolution in the science of astronomy, and proceeded by 

 the sure process of induction, to study the nature of the planets. He 

 selected Mars, because it is nearer us than any of the other planets. 

 He found it impossible that this planet could revolve in a circle of 

 which the sun is the centre, an opinion which had been long enter- 

 tained. Still he was unwilling to abandon the idea, that its orbit 

 was a circle ; and he endeavoured to ascertain, if it might not 

 revolve in a circle with the sun out of the centre. But he could 

 not reconcile its motion even with this supposition. He then banished 

 the idea that its orbit was a circle, and by a fortunate or instinctive 

 guess, concluded that it was an ellipse. Now, this is a very remark- 

 able circumstance, because it varies so very little from a circle, that 

 if it were delineated on paper, it would be impossible so say that it 

 was an ellipse, without very accurate measurement. 



By analogy, he extended the conclusions to which he had come, 

 in regard to Mars, to all the planets. He further demonstrated, 

 that by the planets, equal areas are described in equal times. Newton 

 followed out this law, and shewed that the attracting force diminishes 

 with the square of the distance. He found by reversing this problem, 

 that the orbit must be a curve, of which an oval forms an instance. 



The ellipticity of the orbits, it was shewn, however, does not 

 depend upon physical laws, but upon the will of the Creator, because 

 in proportion to the force with which they were launched into space, 

 they would follow the curve of an ellipse, of a parabola or hyperbola. 



All the planets are collected in the zodiac, from what cause we 

 are not aware, and they all revolve in the same direction. Such are 

 the principal features in the motions of the planets. Now, with re- 

 gard to comets, we find that they differ as much as they possibly can 



VOL. I. 2 H 



