July 14, 1881] 



NA rURE 



•■61 



Special Solar Heat-Radiations and their Earth-felt 



Effects 

 The well-filled lectures on Solar Physics by Prof. Balfour 

 Stewart, published iu Nature, vol. xxiv. pp. 114, 150, will 

 undoubtedly promote the study and afsist the understanding of 

 those subjects ; and if a single one of the many items alluded to 

 was not quite correctly described, that is neither surprising iu 

 itself nor likely to do much liaim amidst the wealth of informa- 

 tion which was at the same time both correctly stated and neatly 

 conveyed. I should not therefore think myself now called on 

 to notice one exceptional paragraph, but that it contains a most 

 singular mistake in attributing to me conclusions from my own 

 Edinburgh observations that are the very opposite of what 1 have 

 often published between 1S69 and the present time. Nor do I 

 propose to make any positive complaint ; for I rather admire the 

 honesty of the lecturer who, after arguing for the n.ore spotted 

 (eriods of the sun's disk beinij its occasions of strongest 

 heat evolutions, yet stated voluntarily and against himself that a 

 directly opposite conclusion to his had been deduced by me from 

 the unrivalled collection of more than thirty years of rock- 

 thermometer observations on the Caltou Hill. That is to s-ay, 

 that a certain eleven-year heat-wave shown by those thermome- 

 ters coincided w ith, not the maximum, but the minimum spotted 

 state of the tun ; subject however to what the lecturer termed 

 "a slight," but in reality a two or three year " lagging behind " 

 the visible solar phenomenon. 



Now let the .-un, at any short-lived epoch, give forth an extra 

 radiation of heat : I cannot imagine any person attempting or 

 expecting to find its effects, after two or three years, as an 

 acutely marked phenomenon in daily air and superficial earth- 

 temperature olservaticns. When therefore a very sharp pheno- 

 menon was marked on, or by, our thermometers, I looked for 

 its explanation, not to what had occurred and pa-sed away again 

 several years before, but to something in nearly simultaneous 

 pro-ress on the sun. This something to'^, which I held forth 

 upon even in my first paper on the subject in 1869 to the Royal 

 Society, was ready at hand as a vera causa ; and I ventured to 

 describe it as " the ascending node" of the eleven-year sun-spot 

 curve, or the time w-hen a new cycle of sun-spots is not only 

 well begun, but is in the act of its most rapid increase f^ r any 

 part of the cycle ; just as a soda-water bottle effervesces most 

 violently immediately after it is uncorked, rather than long after- 

 wards, «hen some of its slowly-formed last bubbles are quietly 

 escaping, and much more so than when it is not uncorked at all. 

 In a letter too, printed in Nature not two years ago, I showed 

 how a great part of the solar action might be, and even h.ad 

 been immediate on our thermometers, in consequence of the very 

 first action of a renovated sun, being a dispersion of the ordinary 

 clouds i}i situ, whence an extra amount of direct sunhine on the 

 earth leneath them, producing a dry hot year to the agriculturi.^ts 

 there. 



The second effects I also showed might be an increased evapo- 

 ration of distant ocean-surface ; the formation thereby and bring- 

 ing round of greater cloud", heavy rain, and precisely the cold 

 seasons which our Edinburgh thennometers had shown, through 

 thirty years, did generally follow the eleven-year w ave of heat. 

 Not, evidently, that the sun was then at a minimum of heat 

 radiation, but that a creen of wet clouds had been drawn 

 between it and that part of the earth where observations were 

 going on. 



Now something like this whole sequence of effects has just 

 1 een experienced in Madeira, all in the course of this week, 

 subsequent to the restored energy of sun-spot manifestation and 

 the earth-answering electric cloud of last Sunday, as I wrote to 

 you next day. 



Now that, or the first day after the specified occurrence, proved 

 scorchingly hot, with a blue sky and the maximum shade 

 temperature of the season, thus far. 



The second day after, a thick screen of clouds was drawn 

 between us and the sun, while the trade-wind was not only 

 restored on the adjacent sea, but with an excess of violence 

 more like that which is felt about Teneriflfe : viz , a more southern, 

 and therefore more sur.-governed, island. 



But the third day after, not only was the sun again totally 

 invisible on account of cloud, but to the surprise of .-ill Madeira 

 there was a heavy, vertical downpour of rain all day long. Old 

 residents protested that they had never, for ten years at least, 

 known anything of the kind at midsummer season. "Precisely 

 so," I replied ; "but in the Cape de Verde Islands still further 

 south, and more under solar dominion than even Teneriffe, you 



will find that every year, the sun coming to the highest northern 

 declination is marked by heavy tropical rains. Wherefore, if 

 Madeira is now visited in the end of June by Cape de Verde 

 solsticial rains, be assured that the sun is at this moment shining 

 above the clouds over Madeira with much more than his usual 

 annual force." 



But though as I « rite, I would seek to draw the attention of 

 your clever lecturer to unUsual solar action being often attended 

 with earth-phenomena which lag behind a few hours only, rather 

 than several years, I do hope he will also obtain a perusal of my 

 paper of 1S69 from the Royal Society, Burlington House, 

 London, and take note of the forty or more year cycle, as well 

 as other shorter ones there alluded to ; for the star.dard eleven- 

 year cycle, of which we have now begun a new example, will 

 never be comjiletely definable without knowing on each occa- 

 sion how fir the others are mixed up with it. Thus we h.id, 

 for instance, in August last year, that eleven -year cycle's 

 maxiiitum of temperature w hich I had pre-announced in print 

 ten years before ; but it was very near being lost to observation 

 by occurring not far from the middle of the long-endiiring 

 minimum of the forty-five years' cycle, whose prime origin is as 

 certainly solar as that of the eleven-year, and even then much 

 shorter cycles of twelve or fifteen days only, of which I have 

 noted several examples since I have been here. 



PiAZZi Smyth, 

 Astronomer-Royal for Scotland 



Jones's Hotel, Quinka do Corvalho, 

 Funchal, Madeir.-i, July 2 



Phenomena of Clouds 



The letter from Prof. Smyth (vol. xxiv. p. 212) recalls to my 

 mind a phenomenon I witnessed several years ago in Arran. I 

 was staying at Strathwhillan, on the north side of Brodick Bay, 

 and looking northward had a full view of Goatfell and Maoldoon. 

 The latter resembles an immense mound he.aped up ag.iinst the 

 eastern side of the former. Snow had recently fallen and coaled 

 both. Then a south-easterly wind, coming up and across the 

 firth, caused a cloud to be formed at a considerable elevation 

 above the hilK-, having its under surface outlined in correct cor- 

 respondence with the outlining of the subjacent mountains. This 

 contour the cloud retained in seeming fixity for several hours. I 

 attributed its continued existence to the effects of unequal radia- 

 tion between the cold snow-covered hills and the warmer moistine- 

 laden current above. Whether my surmise was correct, and 

 whether the "central fixity " over Madeira can be referred to the 

 same cause, I leave to the consideration of those more scien- 

 tifically informed than I. Henry MuiRHEAD 



Cambuslang, July S 



Early English Pendulum Measures 

 I FIND in a volume entitled "iletrology, or Weights and 

 Meaures of Great Britain and France," by P. Kelly, "Master 

 of the Finsbury Square Academy, London," in 1S16, a list of 

 some of the old pendulum experiments of the last century, which 

 contains some indications quite new to me. I am in hopes that 

 if you will allow me space enough to make them known I may 

 perhaps hear where further information is to be found. One of 

 the mea>urements which he of course mentions is that of Graham. 

 It is rather strange that though every one of the old writers 

 mentions Graham's experiments confidently, I have hitheito 

 failed to find any account w hatever of those experiments. The 

 other observers mentioned by Kelly — and so far as I know by 

 him only — are " Emerson," " Desaguillieres " [who always wrote 

 under the name of Desaguliers], " Rotherham, " and " Sir Jonas 

 Moore." The mention is not a mere hears.ay repetition of their 

 names in this connection, as he gives the Itngt/is found by each 

 for London. 



In direct connection I may remark that every one knows that 

 the pendulum has been over and over again mentioned and 

 treated as an ultimate appeal in case of failure of other satisfac- 

 tory means of restoring national standards. In fact its earliest 

 use was for this purpose only — except of course in horology. Is 

 it not then a strange thing that it was nrver — during the whole 

 of the century and a half which so regarded it — used as a 

 medium of comparison of actual national standards ? In Gra- 

 ham's time the relation of the French and English units of 

 measure w as so uncertain that the pendulum, with all its failings, 

 was quite competent to establish a firmer one. Newton's table 



