2 History of physical Science from [July, 



chini of Rome announced, some years ago, that when the violet 

 rays from a prism are drawn along a steel wire for some time 

 always in the same direction, the wire acquires the properties of 

 a magnet. This experiment has been frequently repeated by 

 other persons, but the result has been generally unsuccessful, 

 or at least equivocal. Hence the general opinion at present 

 entertained is, that Morichini has, somehow or other, deceived 

 himself. M. Ridolfi, however, has published a set of experi- 

 ments on this curious subject in' the Journal of Brugnatelli 

 These experiments, if we admit their accuracy, demonstrate the 

 truth of Morichini's statement, and even account for the failure 

 of those who have turned their researches to this subject. 

 Ridolfi made a needle magnetic in 47' by making the violet ray 

 pass continually from the eye to the point. When this needle 

 was suspended, the point always turned towards the north. By 

 making the violet ray pass for 47', over the same needle in the 

 opposite direction, or from the point to the eye, the magnetism 

 was entirely removed. In ten minutes more it acquired the 

 opposite magnetism. The violet ray made to pass for an hour 

 over a weak magnet in the direction opposite to that in which it 

 had received its magnetism, destroyed its magnetic energy 

 altogether. 



According to Ridolfi, the violet ray is incapable of converting 

 a needle into a magnet when the air is moist. This he considers 

 as the reason why so many have been unable to verify the 

 experiment. He even relates a variety of very curious trials 

 which he made on the effect of moisture in this respect. These 

 experiments constitute the most curious part of the memoir. 

 But they would require to be successfully repeated by others 

 before we could^jive their accuracy implicit credit. They seem 

 to point out a iw? analogy between magnetism and electricity.* 



2. Next to the mathematical theory of heat, published at 

 Paris in a quarto volume by M. Fourier, f the most important, 

 addition to this intricate, but essential department of chemistry, 

 is the Recherches sur la Mesure des Temperatures et sur les Lois cle 

 la Communication de la Ckaleur, by MM. Dulong and Petit, 

 which gained the physical prize voted by the French Academy 

 of Sciences on March 16, 1818. Mr. Dalton, in the first part 

 of his System of Chemistry, had given it as his opinion that 

 bodies expand as the square of the temperature, reckoning from 

 the point of their maximum density. This opinion induced him 

 to propose a new thermometrical scale, which he considered as 

 correct, and as removing the ambiguities and apparent anomalies 

 which have hitherto perplexed the investigations of those who 



» The experiment has been lately performed with success by M. Carpe, at 

 Geneva, in the presence of Prof. PJayfair. — See Annals of Philosophy for 

 May, 1818.— Ed. 



+ This v. ork is the result of a long continued investigation, and is highly worthy 

 cf the attention of chemists. 



