26o 



NATURE 



\_7an. 31, 1878 



istic year, or the time which elapses between two perihelion 

 passages. 



Prof. Wolf and Messrs. De la Rue, Stewart, and' Loewy have 

 all distinctly stated their belief that Jupiter is the chief cause in 

 the production of sun-spots. This 1 1 '9 years' period will then, 

 I believe, remove what little doubt remains in some minds on 

 the subject. Mr. John Allan Broun, F.R.S., has already shown 

 in Nature (vol. xvi. p. 62) that Dr. Wolf, to be consistent 

 with his own relative numbers, ought to take a period of 1 1 94 

 years rather than one of ll'l, and while be himself favours a 

 10 5 years' period, he admits that there is no combination of 

 planetary positions which would produce such. 



I may perhaps be allowed to state here that in a paper I have 

 just forwarded to the Royal Astronomical Society I have given 

 what I believe are satisfactory reasons for the variations of these 

 curves, and such as will enable us for the future to calculate with 

 considerable accuracy the lengths of the periods, and guided by 

 these reasons I have ventured to state my belief that we are now 

 passing through a long minimum-period — one very similar to that 

 which occurred at the close of the last centurv, and that the next 

 maximum of sun-spots will fall in the year 1887. 



I make this statement from an examination of the causes which 

 produce the 'sun-spots ; and it is so far remarkably confirmed by 

 the behaviour of the magnetic needle. Mr. Broun, in Nature, 

 vol. xvii. p. 183, speaking of the very gradual manner in which 

 the curve has been going to a minimum during the last three and 

 a half years, remarks that "no such constant state of the sun's 

 magnetic action will have been observed since the last years of 

 the eighteenth century." To this I would add that immediately 

 prior to the commencement of that long sun-spot minimum 

 period, the mean of the magnetic interval, which occurred then 

 (reckoning the interval from minimum to maximum), fell in the 

 year 1785, and corresponded with the time of Jupiter's perihelion 

 passage. Suppose now we represent this synchronism by o, it 

 will be found that the mean point in the next period lagged 

 behind the perihelion i"6 year; next, 5 '3 years; next, 5 '3 

 years. Having reached its maximum of lagging, in the next 

 period it lagged 3*9 years ; next, l*2 year ; next, o"6 year ; and 

 in the last period the mean point fell in the year 1868, coinciding 

 for the first time since 1785 with Jupiter's perihelion, and will 

 be represented by o. So that the magnetic oscillation in 1868 

 was just where it was in 1785. Is it rot a natural inference, 

 then, that we have commenced another cycle of magnetic 

 declination ? 



What produces this lagging? This is a veiy important 

 question, and one which 1 have reason to believe can be satis- 

 lactorily answered. B. G. Jenkins 



January 19 



On a Means for Converting the Heat Motion Possessed 

 by Matter at Normal Temperature into Work 



My attention has just been directed to Mr. S. Tolver Preston's 

 two papers in Nature, vol. xvii. p. 31 and p. 202, in which he 

 points out what appears to be an exception to the second lawlof 

 thermodynamics. Some years ago I illustrated the same subject 

 in a somewhat different manner by an experiment which is in 

 some respects better suited for lecture purposes, and while the 

 subject is beng considered may be useful to your readers. 



Into the cork of a large bottle were fitted two glass tubes. 

 One tube went to the bottom of the bottle, its upper end being 

 terminated in a fine jet. The other tube only passed a short 

 distance into the bottle, and its upper end terminated about an 

 inch above the cork. To its lower end was fixed some pieces of 

 blotting-paper, to its upper end was attached a small test-tube, 

 the two being connected by means of a piece of india-rubber 

 tube. Some water was put in the bottle and the cork fitted close 

 in its place. The test-tube was then filled with ether or some 

 volatile fluid, and fitted to the end of the india-rubber tube. 



After the apparatus had attained a uniform temperature, the 

 test-tube was inverted, so as to cause the ether to flow down the 

 tube, and enter the bottle, where it spread itself over the blotting 

 paper and, rapidly evaporating, produced a pressure inside the 

 bottle. The addition of the ether vapour to the air already at 

 atmospheric pressure, produced a pressure sufficient to force the 

 water up the t»be and out of the jet, causing it to rise to a con- 

 siderable height into the air. At the beginning of the experiment 

 all the apparatus was at a uniform temperature, and, according 

 to the generally received opinion, ought to have been incapable 

 of developing energy, yet op account of the ether vapour not 



being diffused through the system, it was able to do work at the 

 expense of part of the heat in the system. John Aitken 



Darroch, Falkirk, January 18 



No Butterflies in Iceland 



Allow me to point out that the lepidopterous insects said by 

 Olafsen (not Olaffson) and N. (not R.) Mohr, to be found in 

 Iceland, are not butterflies at all, but moths, as shown by the 

 generic term Phalcsna applied by each of those authors to every 

 one of them — a term whose meining your correspondent and his 

 informant have failed to see. Those venerable authors, though 

 dead and buried long before I ever heard of them, are old 

 friends of mine, and I feel it incumbent on me to ask your 

 readers not to impute to them this and other mistakes in Dr. 

 Rae's letter. Whether there have been or still be butlerflies in 

 Iceland I am not competent to declare. I did not see any 

 when I was there, but they may have got out of my way. I 

 have, however, yet to learn that they exist in that country, and 

 therefore I am inclined to believe Mr. McLichlan is right when 

 he said that there are none. We have the testimony of the 

 late Sir William Hooker (" Tour," &c., ed. 2, vol. i. p. 333) that 

 no butterfly had ever been met with in Iceland up to 1809, the 

 year in which he visited that island. Gliemann (" Geogr. 

 Beschreib. Isl.," p. 165) in 1824 was unable to add to Mohr's 

 list of twelve species of moths, and included no butterflies. If 

 any of the latter have since been found ic would be well for Dr. 

 Rae to give his authority for the fact, otherwise hii ingenious 

 supposition that Icelandic butterflies and their larvte have been 

 destroyed since 1786, is unnecessary, and his "only possible 

 way" of reconciling "perfectly opposite authorities" falls to the 

 ground through the absence of any opposition on the part of the 

 authorities he has cited. Alfred Newton 



Magdalene College, Cambridge, January 25 



[Dr. Rae writes "to explain and correct a mistake which, by 

 a little care and attention on my part could and should have 

 been so easily avoided."] 



On some Peculiar Points in the Insect-Fauna of Chili 



My friend Mr. Birchall misconstrued the meaning of my 

 notes (Nature, vol. xvii. p. 162) in a manner incomprehensible 

 to me, when penning his own (p. 221). I, and many others, 

 will share his " surprise " when he can produce any species ot 

 the genera Carabus, Argynnis, and Cohas, or any of the Livino- 

 philidcE from Australia or New Zealand. If he will do me the 

 favour to again read my notes he will find that I refer solel/ 

 to Palaearctic and Nearctic forms occurring in the Chilian sub- 

 region and (unless by exception) nowhere else in the southern 

 hemisphere. 



Mr, Wallace's rebuke (p. 182) is to some extent merited. I 

 did not give sufficient attention to the chapter in his work, to 

 which he refers, in consequence of its general character. Mr. 

 Wallace greatly extends the number of genera published by me 

 as a sample. Some of these were perfectly familiar to me ; other.s 

 I think, will fail to stand the test of minute application, partly 

 because their distribution is more extended, partly because generic 

 definitions are vague. I could add several interesting and marked 

 genera. Colias may possibly be represented by more than one 

 species on the Norttiern Andes; but it is the opinion of naturaliits 

 who, from practical acquaintance with the fauna of South America, 

 and who, on a special point like this, are more competent tliarr 

 I to judge, that most of the very marked forms upon which I 

 especially rely do not occur on the Northern Andes, which of 

 late have been most assiduously worked by entomologists hunt- 

 ing insects for sale and perfectly alive to the value of such 

 forms. 



Mr. Darwin's theory alluded to by Mr. Birchall had not been 

 overlooked. I was dealing with insects, and with a few marked 

 genera, &c., of them, only. In plants there appears to be a 

 tendency towards the appearance of analogous or identical forms 

 all over the world when a sufficient altitude (varying accordmg 

 to the latitude) is reached. The laws that govern the dis- 

 tribution of the one ought equally to affect the other. Still the 

 facts alluded to in my former letter remain unexplained. The 

 southern portion of South America forms, as it were, an island, 

 with a large admixture of Palaearctic and Nearctic faunistic 

 elements existing in no other part of the southern hemisphere. 



Lewisham, January 19 Robert McLachlan 



