204 



largest ; the equatorial diameter the next ; and the polar diameter 

 the smallest. 



June 1. Two measures of the latitude of the greatest curvature 

 were taken, by setting the fixed thread of the micrometer to the di- 

 rection of the ring. The mean of these was 43 20'. 



June 2nd. The two planets were viewed alternately, with powers 

 of 300, of 200, and of 1 60 ; and even with the lowest of these, the 

 difference in the figure of the planets was very evident. 



The telescopic appearance of Saturn was then compared with a 

 figure drawn from the measures Dr. Herschel had taken, combined 

 with the proportion between the equatorial and polar diameters de- 

 termined in the year 1789. From these a corrected figure was 

 formed, of which an exact copy is given. The dimensions of it, in 

 proportional parts, are, 



Diameter of the greatest curvature 36 



Equatorial diameter 35 



Polar diameter 32 



Latitude of the longest diameter 43 20' 



These observations, Dr. Herschel thinks, may tend, in some mea- 

 sure, to ascertain the quantity of matter in the ring and its solidity ; 

 they also afford a new instance of the effect of gravitation on the 

 figure of planets ; for in the present case the opposite influence of 

 two centripetal, and two centrifugal forces, must be considered. 



On the magnetic Attraction of Oxides of Iron. By Timothy Lane, 

 Esq. F.R.S. Read June 20, 1805. [Phil. Trans. 1805,^. 281.] 



Mr. Lane having observed that hardened iron is not so readily at- 

 tracted by the magnet as soft iron, was proceeding to make some 

 experiments on the subject, when he was led, by Mr. Hatchett's paper 

 on Magnetical Pyrites, &c., to examine what magnetical properties 

 iron possessed when free from inflammable matter. For this purpose 

 he procured some of the precipitate sold at Apothecaries' Hall under 

 the name of Ferrum precipitatum, and which is prepared by adding 

 purified kali to a solution of sulphate of iron. This precipitate, the 

 author says, has no magnetic particles ; nor, when exposed to a clear 

 red heat, does it acquire any, except when smoke or flame have access 

 to it. The solar heat, when concentrated to the degree at which 

 glass melts, does not render this oxide magnetic, provided it be pro- 

 tected by glass from the dust floating in the air ; if not so protected, 

 many of the particles become magnetic. 



Mr. Lane then rubbed various portions of the oxide, in a glass 

 mortar, with different combustible substances, namely, coal, sulphur, 

 charcoal, camphor, ether, alcohol, &c., but found the oxide was not 

 thereby rendered magnetic, without the assistance of a degree of 

 heat equal to that of melting lead ; with that degree, however, it 

 became magnetic. Hydrogen, when aided by a red heat, had the 

 same effect. Charcoal and cinders, well burnt, were found to re- 

 quire a longer continuance of the heat, to have their full effect on 



