263 



where there is a large venous plexus, corresponding to the site of the 

 tadpole's gills, and seeming to indicate that the subcutaneous distri- 

 bution of the second branch of the pulmonary artery may further aid 

 the office of the lungs by bringing the blood to the surface to be 

 acted on by the air. 



The author concludes this paper by stating, that he has endeavoured 

 to trace a direct Communication by spiracula through the integuments, 

 but has only obtained negative results, never having succeeded in 

 forcing the smallest bubble of air through the skin. 



. On the magnetizing Power of the more refrangible Solar Rays. By 

 Mrs. M. Somerville. Communicated by~W. Somerville, M.D. F.R.S. 

 February 2, 1826. Read February 2, 1826. [PAi7. Trans. 1826, 

 Part II. p. 132.] 



In the year 1813, Professor Morichini, of Rome, announced that 

 steel exposed in a particular manner to the concentrated violet rays 

 of the prismatic spectrum becomes magnetic. His experiments, how- 

 ever, having uniformly failed in other hands, had ceased to excite gene- 

 ral attention ; especially in this country, whose climate is usually so 

 unfavourable for such researches. The unusual clearness of weather 

 last summer, however, induced Mrs. Somerville to make the attempt. 

 Having, at that time, no information of the manner in which Prof. 

 Morichini's experiments were conducted, it occurred to her, however, 

 as unlikely that if the whole of a needle were equally exposed to the 

 violet rays, the same influence should at the same time produce a 

 south pole at one end, and a north at the other of it. She therefore 

 covered half of a slender sewing needle, an inch long, with paper, and 

 fixed it in such a manner as to expose the uncovered part to the vio- 

 let rays of a spectrum, thrown by an equiangular prism of flint glass 

 on a panel at five feet distance. As the place of the spectrum shifted, 

 the needle was moved so as to keep the exposed part constantly in 

 the violet ray. The sun being bright, in less than two hours the 

 needle, which before the experiment showed no signs of polarity, had 

 become magnetic ; the exposed end attracting the south pole of a 

 suspended magnetic needle, and repelling the north. No iron was 

 near to disturb the experiment, which was repeated the same day, 

 under similar circumstances, with a view to detect any source of fal- 

 lacy in the first attempt, but with the same result. 



The season continuing favourable, afforded daily opportunities of 

 repeating and varying the experiment. Needles of various sizes (all 

 carefully ascertained to be free from polarity), and exposed in va- 

 rious positions with regard to the magnetic dip and meridian, almost 

 all became magnetic ; some in a longer, some in a shorter time, va- 

 rying from half an hour to four hours, but depending on circum- 

 stances not apparent. The position of the needles seems to have 

 had no influence, but the experiments were generally more success- 

 ful from 10 to 12 or 1 o'clock than later in the day. The exposed 

 portion of the needle became (with a few exceptions) a north pole, 



