Jnne 28, 1877J 



NA TURE 



171 



winding up with a trip round the harbour.'with its men-of- 

 war, doclcyards, forts, and factories. The Government 

 establishments are ahvays open to English folk. Our 

 foreit;n friends who may desire to go over them, will have 

 to provide themselves with a special order. There will 

 be also a trip to Liskeard, for the Caradoc and Phcenix 

 mines, and the famous Cheesewing. As mining is the 

 special industry of Cornwail, and to a great extent of 

 South Devon, it has been thought desirable to have two 

 mining excursions — one on each day. South Caradoc is 

 one of the richest copper mines in Cornwall ; Phoenix is 

 a tin mine ; and both are admirably managed and excel- 

 lently adapted to illustrate raining operations. The 

 mineralogy of this district has some peculiar features. 

 Phoenix has lately yielded the rare minerals chalcosiderite, 

 andrewsile, and the beautiful turquoise-hued henwoodite. 

 The third excursion will be to the Lee Moor China clay 

 works. These are situated on the skirts of Dartmoor, not 

 far from Plympton, are of immense size, and afford pro- 

 bably the best illustration of this great industry, which 

 Cornwall and Devon owe to the researches and ingenuity 

 of Cookivorthy, chemist and potter, manufacturer in the 

 Plymouth china of the first true English (hard) porcelain. 

 It is likely that this excursion will be taken up by the 

 Plymouth Institution, and so arranged as to embrace a 

 visit to Princetown, and its convict prison, and some of 

 the fine prehistoric antiquities of Dartmoor; if not there 

 will probably be an e.'ctra excursion with this object given 

 by the institution. 



Thursday will be a long day, and wholly given up to 

 excursion pleasures. The mining excursion will be up 

 the lovely river Tamar to Devon Great Consols, which 

 communicates by a railway of its own to shipping quays 

 at iMorwcllham, in the close vicinity of the most pic- 

 turesque scenery of the Tamar valley. On the way, by 

 the kindness of the Countess Dowager and the Earl of 

 Mount-Edgcumbe, the party will have an opportunity of 

 inspecting Cotehele, one of the most perfect examples of 

 a media:val mansion now extant. At Devoa CoiiSols — 

 not long since the largest and richest copper mine in the 

 land, which gave in dividends considerably over a million 

 — not only are mining operations conducted on the most 

 extensive scale, but there are enormous arsenic works, 

 huge water-wheels, and many other objects of interest. 

 The other excursions arranged for the day are to Torquay 

 and Penzance. The good people of Torquay intend to 

 follow the capital precedent set in 1869, and to invite and 

 entertain a number of guests. Eit route from Plymouth 

 a steamer trip may be made down the lovely river Dart ; 

 and at Torquay thcfe are plenty of objects of interest. 

 The Torquay Natural History Society has a well-stored 

 museum ; Kent's Cavern is of course a museum in itself, 

 with a very Cerberus of a curator in Mr. Pengelly ; and 

 then there are the works of Mr. Froude, F.R.S.,at Chelson 

 Cross, where he conducts those delicate experiments for 

 the Admiralty on the forms of ships and their properties 

 of stability, and to which he intends to invite members of 

 the Association who are specially interested in this branch 

 of mechanical science. Steps are, we believe, being taken 

 at Penzance to give the excursionists thither a hearty 

 welcome. The museums of the Penzance Natural History 

 Society and of the Royal Geological Society of Cornwall, 

 the latter of which contains the best public mineralogical 

 collection in the West of England will be thrown open 

 to them, and excursions in all probability organised to 

 the chief attractions of the neighbourhood. It is hoped 

 to provide special railway facihties for those who may 

 wish to visit other parts of the country — such as Tintagel 

 or the Lizard, or the western mining district. At Truro 

 is the excellent museum of the Royal Institution of Corn- 

 wall, which will be open to visitor;. 



The former meetmg at Pl> mouth, of the Association, 

 was in 1841, with Dr. Whewell, as president, and was a 

 very successful gathering. Six-and-thirty years are a long 



time, and it is remarkable that so many who took a pro- 

 minent part on that occasion are yet with us. One of 

 the vice-presidents still survives — the Earl of St. Gar- 

 ni ms ; two of the local secretaries, Mr. R. W. Fox, F.R.S., 

 and Mr. R. Taylor, F.G.S. ; a vice-president of the 

 statistical section, the Earl Fortescue, then Viscount 

 Ebrington ; Dr. Owen, F.R.S., vice-president for Zoology 

 and Botany ; and Mr. Robert Hunt, F.R.S., then secre- 

 tary of the section of Chemistry and Mineralogy, are still 

 with us. There will not be wanting opportunity, there- 

 fore, of comparing personal experiences in 1841 and 

 1877. 



INDIAN RAINFALL AND SUN-SPOTS 



C'\ N May 24 Gen. Strachey read a paper before the Roval Society 

 ^-^ entitled " On the alleged Correspondence of the Rainfall at 

 Madras with the Sun-Spot Perio !, and on the True Criterion of 

 Periodicity in a Series of Variable Quantities." 



He stated that a paper hail recently been printed by Dr. 

 Hunter, the Difector-General of Statistics to the Government of 

 India, having for its object to show that the records of the rain- 

 fall at Madras, for a period extending over sixty-four years, 

 establish a cycle of rainfall at that place which has a marked 

 coincidence with a corresponding cycle of sun-spots — the rainfall 

 and sun-spots attaining a minimum in the eleventh, first, and 

 second years, and a maximum in the fifth year. 



Tiie Madras register extends over sixty-four years, beginning 

 with 1813. The mean rainfall (or the whole period is 48'S 

 inches. The deviations from the mean vary from 30' i inches in 

 dei;ct to 39 9 inches in excess. The arithmetical mean of these 

 deviations (disregarding the signs) is 124 inches. 



Dr. Hunter divides the sixty-lour years' observations into six 

 cycles of eleven years, and calculates the arithmetical mean of 

 the successive years of the whole series of cycles. The results 

 are as follows : — 



In the above calculation the first year of the cycle of eleven is 

 1813, so that the average period of maximum sun-spots will be 

 about the third or fourth year of the cycle, and the period of 

 minimum will be about the tenth or eleventh of the cycle. This 

 table apparently indicates a period of maximum between the 

 third and the seventh years, and of minimum between the eighth 

 and the second years. 



But as the only signification of the arithmetical mean value of 

 a series of observed quantities is that it is one above and below 

 which there is an equal amount of deviation in the individual 

 observations, the question whether or rot the mean values thus 

 obtained can be accepted as showing a definite law of variation 

 from ye3r to year in the cycle must be determined by examining 

 the differences between those means and the individual observa- 

 tions on which they are based. 



Treating the observations in this manner, it appears that the 

 mean difference of the individual observations from the means 

 shown in the table amounts to 11 '2 inches, and differs but 

 little from the mean difference of the indivioual observations from 

 the arithmetical mean of the whole series. In other words, 

 the supposed law of variation obtained from the means of the 

 six eleven-year cycles hardly gives a closer approximation to the 

 actual observations than is got by taking the simple aiithmetical 

 mean as the most probable value for any year. 



In order to obtain a practical test of the probable physical 

 reality of the cycle of eleven years, the author calculated a ser ies 

 of mean values corresponding to those given in the table for a 

 series of cycles of five, six, seven, eight, nine, ten, twelve, and 

 fourteen years. The mean differences between these means an 

 the observed quantities are all within a very small fraction of o 

 nnolher, and of the mean obtained from the eleven-year cycle— 



