316 Scientific Intelligence, 6fc. 



box formed of a double bar of iron and brass, which opens in propor- 

 tion to the temperature. Dr. Arnot finds that it requires no atten- 

 tion, that a sufficient quantity of fuel deposited in the furnace in the 

 morning lasts for 24 hours, and thus produces a very great saving 

 of fuel. The heating surface may be increased by having two or 

 more of these boxes at any distance connected by tubes. Dr. Arnot 

 described a method of ventilating rooms by having two parallel 

 tubes, one of them supplied with a fanner to extract the air, and 

 the other with a simular contrivance to force in air. 



VI. — Magnetic characters of the Metals. 

 The opinion of Dr. Faraday, as stated at the Royal Institution in 

 reference to the metals, is, that they are all magnetic, just as they 

 are all capable of being solidified, but that a proper temperature is 

 the desideratum, as with mercury, for the solidification of which a 

 low temperature is required. The analogy is principally derived from 

 the case of iron which loses its magnetic power at an orange heat, 

 and when cooled down regains its attractive power. Nickel exhibits 

 similar properties. When heated and cooled, it retains its negative 

 state long after it has ceased to be visible in the dark. Even when 

 emersed in hot almond oil it loses its magnetic power. This point 

 appears to be between 630° and 640°. Cobalt and chromium are stated 

 in chemical works to be magnetic. Dr. Faraday found that specimens 

 of these metals, which were said to be magnetic, derived that property 

 from the presence of iron or nickel. The result of his experience 

 in respect to chromium is similar to that of Dr. Thomson, who long 

 ago determined that it was not magnetic. Dr. Faraday endeavoured 

 to excite the magnetic power in a number of metals by sinking their 

 temperatures to 60° and 70°, but could not succeed ; nevertheless, 

 he is convinced that the only desideratum, in reference to the de- 

 velopement of magnetism in all metals, is the particular magnetic 

 temperature. 



VLI.—HaUet/'s Comet. 

 This remarkable visitor was first seen in the beautiful sky of Italy, 

 on the 5th of August last, at the Observatory of Rome, by Dumouchel 

 and Vico. Its position then, was near ( of the Bull. On the 21st 

 of the same month, it was observed at Paris, Breslaw, and .Naples; 

 on the 22nd at Vienna and Berlin ; 23rd at London ; 24th at Nimes ; 

 26th at Dublin ; 27th at Florence and Bologna ; 31st at Yale Col- 

 lege, Newhaven, in North America, by Professor Olmsted and Tutor 

 Loomis, its right ascension, being by observation, 5 h. 50 - 5 m., and 

 its declination N. 24° 46'*8 ; on the 1st September at Turin and 

 Geneva. By a letter, dated Madras, 27th September, which I have 

 received, it appears, that " no trace of the mysterious body can be 

 found."* It was seen by the naked eye at Paris on the 23rd Sept. 

 and at Geneva on the 24th. On the 15th October, with the naked 

 eye, the tail of the comet embraced an extent of 20°, but on the 16th, 

 it appeared to extend only 10° or 12°. On the 30th, it was very 



* It was risible in the Bombay presidency on the 6th October. — Edit. 



