290 Messrs. J. H. Gladstone and A. Tribe on the [Apr. 11, 



III. Corrective Note by Messrs. De La Rue, Stewart, and Loewy to 

 their Paper " On some recent Researches in Solar Physics &c/ ; * 



The erroneous date given in our paper for one of Professor "Wolf's 

 maxima has already been corrected by us, and we give in the subjoined 

 little Table the corrections of the few numerical data which are necessitated 

 by the error of fixing the date of maximum at 1846*6 instead of 1848*6. 



Professor Wolfs ratio A (p- 86). 



Erroneous figures given previously. 



Differences. 



I. 1*265 ) -0*728 

 II. 2*615 I Mean 2*093 + 0*522 

 III. 2*400 J +0*307 



Corrected figures. 



Differences. 



1-265 ] +0-283 

 1-478 I Mean 1-548 +0-073 

 1-900 J +0-352 



The differences derived from our own results are respectively +0*061, 

 — 0-107, and +0*047, that is, they are still much smaller, and agree 

 singly better with the mean, than if Professor Wolf's ratio were adopted ; 

 hence our conclusion is quite unaffected by this correction. 



The remark made by us with reference to this maximum (vide p. 85) 

 will remain in force even with the corrected date. We stated there that 

 this particular maximum showed alone an appreciable difference from the 

 dates fixed by ourselves, for it will be found that Professor Wolf's date 

 differs still by about f of a year from ours. 



IV. "The Action of Oxygen on Copper Nitrate in a state of tension." 

 By J. H. Gladstone, Ph.D., F.R.S., and Alfred Tribe, 

 E.C.S. Received March 14, 1872. 



In our experiments on the action between copper and nitrate of silver in 

 solution, we frequently noticed that the tips of the silver crystals became 

 red, as though coated with a thin layer of metallic copper. 



This apparent deposition of a positive on a more negative metal of course 

 raised our curiosity, and led us to look closely into the circumstances 

 under which it occurred. We found that it took place only when the 

 nitrate of silver was exhausted, and only on those silver crystals which 

 remained in metallic connexion with the copper. We found, too, that the 

 cupreous coating formed most readily where air had the freest access, and, 

 in fact, that it would not form at all in vessels from which oxygen was 

 excluded, nor on those white crystals which were far below the surface of 

 the liquid, though they might be in immediate contact with the copper 

 plate. When an inverted jar was filled with nitrate-of- copper solution and 

 silver crystals resting on branches of copper, and the liquid was displaced 

 by oxygen gas, it was found that the tips of the crystals became red, and 



* Suprfr, p. 82. 



