82 Messrs. Warren De La Rue, Stewart, and Loewy [Dec. 21, 



Schwanert * gives as 134°*3. The /3 pyromucic acid from fucusol crys- 

 tallizes from its aqueous solution in small rhomboidal plates, whilst the 

 acid which I had prepared from furfurol crystallized in flat needles. 



Silver /3 pyrornucate. — This compound was prepared from the pure 

 /3 acid by boiling it for a short time with silver oxide and a sufficient 

 quantity of water, filtering, and setting aside to crystallize. A single re- 

 crystallization from boiling water, in which it is only moderately soluble, 

 rendered it quite pure. On cooling the hot aqueous solution, the silver 

 j3 pyrornucate is obtained in long flat needles, whilst the corresponding 

 salt of the ordinary acid forms small crystalline scales : *505 grm. of silver- 

 salt gave *330 grm. argentic chloride, which corresponds to 49*18 per 

 cent, of metallic silver ; the formula C 3 H 3 Ag0 3 requires 49*32 per cent. 



From this silver determination it will be seen that this compound is 

 isomeric with the ordinary silver a pyrornucate, C 5 H 3 Ag0 3 . 



III. " On some recent Researches in Solar Physics, and a Law regu- 

 lating the time of duration of the Sun-spot Period." By Warren 

 De La Rue, D.C.L., F.R.S., Balfour Stewart, F.R.S., and 

 Benjamin Loewy, F.R.A.S. Received October 12, 1871. 



1 . In the short account of some recent investigations by Professor Wolf 

 and M. Fritz on sun-spot phenomena, which has been published lately in 

 the 'Proceedings of the Royal Society* (1871, vol. xix. p. 392), it was 

 pointed out that some of Wolf's conclusions were not quite borne out by 

 the results which we have given in our last paper on Solar Physics in the 

 Philosophical Transactions for 1870, pp. 389-496. A closer inquiry into 

 the cause of this discrepancy has led us to what appears a definite law, 

 connecting numerically the two branches of the periodic sun-spot curve, 

 viz. the time during which there is a regular diminution of spot-produc- 

 tion, and the time during which there is a constant increase. 



It will be well, for the sake of clearness, to allude here again, as briefly 

 as possible, to Professor Wolf's results before stating those at which we 

 have arrived. 



2. Professor Wolf had previously devoted the greater part of his laborious 

 researches to a precise determination of the mean length of the whole sun- 

 spot period, but latterly he has justly recognized the importance of obtain- 

 ing some knowledge of the average character of the periodic increase and 

 decrease. Hence he has, as far as he has been able to do so by existing 

 series of observations, and his peculiar and ingenious method of rendering 

 observations made at different times and by different observers comparable 

 with each other, endeavoured to investigate more closely the nature of the 

 periodic sun-spot curve by tabulating and graphically representing the 

 monthly means taken during two and a half years before and after the 



* Ann. Chem. Pharm. vol. cxvi. p. 257. 



