Effect of Cvld on the Magnetic Fluid, 1 99 



Hoping tlie few observations I have contented myself with 

 making on the defects of the article Observatory in this valu- 

 able Encyclopedia will find a place in your Magazine, and 

 produce a good effect, I remain, gentlemen, 



Yom" obedient servant, 



Sept. 1822. A.M. 



XXXVII. A Letter ^oP/-o/t'5sor Millington, of the Royal In- 

 stitution, respecting some Frigori/ic Experiments made on the 

 Magnetic Fluid, and on Sea- Water. By B.De Sanctis, M.D.* 



Sir, — i.HE magnetic experiments of yesterday which I had 

 spoken of to you the day before, have been successful beyond 

 our most sanguine expectations. Mr. Gary (Strand), in whose 

 house they were made, took a very active and intelligent part 

 in them. But had you been present, as we expected, they would 

 have been much more agreeable to us. Between two hollow 

 parallelopipeds of laminar copper, four inches in length, four 

 ditto in breadth, and one inch in depth, filled with ice and 

 muriate of lime, and rendered air-tight by greased covers, the 

 thermometer F being placed across them and the bulb resting 

 on the cover of one of tliem, marked 40, the magnetic action 

 of a common arrow-shaped needle, two inches long, 1-16 ditto 

 ui the greatest breadth, weighing with the brass cap 7^ grs., 

 was greatly paralysed in the open aii", and also under the glass 

 of the air-pump, and much more during and after exhaustion, 

 when it stood still. The centre of the needle was at half the 

 height of the parallelopipeds, and nearly at the distance of an 

 inch and an half. Two other needles of die same shape, but 

 three inches long, l-8th in the greatest breadth, and weighing 

 with the brass cap 11^ grs., showed still less activity, but not 

 so much as the other. In trying a new needle, it was necessary 

 to allow it suflicient time to adapt itself to the lower degree of 

 temperature before it exliibited ihejmralysis of its forces. By 

 this word I understand its being less sensible, or even alto- 

 gether insensible, to the bai- at the same distance and direction, 

 and its sluggishness hi returning to its former position, if it ever 

 does so. The extremes of the scale of temjierature, the ther- 

 mometer being placetl as before, were from 30 deg, at the mor 

 ment of the most perfect vacuum to 40 deg. in the open air. 

 Comparative observations on a more extemled and detailed 

 scale of temjierature, ))articularly in vacuo, would be an in- 

 teresting ac(|uisiUon, and so much the more, as suflicient atten- 

 tion lias not been paid to the temperature, when it has been said 



* Communicated by Mr. Cary. 



that 



