VOL. LXXVI.] PHILOSOPHICAL TRANSACTIONS. 57 



pears as a star of between the 4th and 5th magnitude, if not nearer the 5th ; and 

 its relative brightness is as follows : nearly equal to i and ^ Cephei, and consi- 

 derably less than 7 Lacertae. Some observations of Mr. Pigott's are also given, 

 which tend to confirm the results above given. 



Mr. G. then adds, that the greatest brightness of S Cephei does not seem to be 

 always quite the same, is not peculiar to this star, but is also to be observed in 

 the other variable ones. He remarked in a late paper, that the greatest bright- 

 ness of |3 Lyrae is subject to considerable alterations, and thought then that it 

 might be owing to some fallacy of observation ; but now he alters, in some mea- 

 sure, his opinion on this head. Even Algol does not seem to be always obscured 

 in the same degree, being perceived to be sometimes a little brighter than ^ Persei, 

 and sometimes less than it. These seeming irregularities however do not appear 

 to affect the period ; for if the same precise phases are compared together, it will 

 be found still regular. This he supposes may be accounted for, by a rotation of 

 the star on its axis, having fixed spots that vary only in their size. 



III. Magnetical Experiments and Observations. By Mr. T. Cavallo, F.R.S, 

 being the Lecture Jounded by the late Henry Baker, Esq. F. R. S. p. 62. 



The object of this lecture is to show the properties of some metallic substances 

 with respect to magnetism ; and the experiments here related, says Mr. C, seem 

 to ascertain some new and remarkable facts. The magnetic properties have been 

 generally thought to belong only to iron, or to those substances which contained 

 that metal ; comprehending under the general name of iron not only the metal, 

 commonly so called, but also its more perfect and more imperfect states, viz. steel 

 iron ores, among which is considered the magnet, and the calces of iron, except- 

 ing only those which are very much dephlogisticated, for they possess no magnetic 

 property whatever. Some other metallic substances, and especially platina, brass, 

 and nickel, on which the magnet has some action, were thought to be magnetic 

 so far as they contained some portion of iron, the presence of which may be ma- 

 nifested by chemical methods in many cases, but not always ; because the quan- 

 tity of iron may be so very small in proportion to the weight of the other metal in 

 which it is concealed, as not to be discoverable by chemical analysis, and yet it 

 may be sufficient to affect the magnetic needle. The following experiment will 

 show, that an exceedingly small quantity of iron will render a body sensibly 

 magnetic. 



Having chosen a piece of Turkey-stone, which weighed about an ounce, I 

 examined it by a very sensible magnetic needle, and found that it had not the 

 least degree of magnetism, the needle not being moved from its usual direction 

 by the vicinity of any part of the surface of the stone ; I then weighed a piece of 

 steel with a pair of scales that turned with the 20th part of a grain, and afterwards 



VOL. XVI. I 



