562 



NATURE 



\OcL 2 2, 1874 



maximum of the year 1 790 to that of 1 850, was thence concluded, 

 perhaps too confidently, as the real length ot this long cycle of 

 anroral frequency. . ^ it 



On turning to Kcemtz's " Meteorology ' (translation by C. V. 

 Walker, 1S48, p. 458), I find that the author, with his usual ex- 

 haustive completeness, has constructed a general list of auroras 

 observed up to his time (about the year 1S20), and has esta- 

 blished from it certain laws of their periodicity. The list itself, 

 although not given for brevity in the tranajation, is in all 

 probability contained in the original, and it must embrace up- 

 wards of 3,000 cases of auroral occurrences, since a tible of 

 about that total sum showing the numbers recorded in each of 

 the several months of the year is given as the most important 

 scientific result of the compilation. The numbers seen in March, 

 September, and October are about half as great again as those 

 recorded in any of the adjacent months, and about twice as 

 great as have been recorded in either of the two mid-winter 

 months of December and January, when the length of the niglits 

 is yet most favourable for their registry. That the numbers of 

 auroral displays noted in June and July are relatively very small 

 is easily explained by the lengtli of the twilight iu those months 

 in European latitudes, rendering many, that would be conspicuous 

 exhibitions in darker nights, invisible. 



The times of greatest annual activity of the aurorse are thus 

 about the seasons of the equinoxes, when the seat of the most 

 direct action of the sun's rays upon the earth's surface is under- 

 going its most rapid changes during the sun's yearly course ; and 

 when nearly the same parts of the earth's surface continue to be 

 heated directly by the sun's rays at the seasons of the winter and 

 summer solstices, there are times of comparative repose and 

 tranquillity among the exhibitions of auroral outbreaks. 



Regarding a secular period, Kxmtz's Catalogue appears to 

 have shown nothing positive. ''A period of this kind," he 

 write-, "occurred between the years 1707 and 1790, attaining 

 its maximum about the year 1752 ; since the year 1S20 they have 

 ao-ain continued to become more numerous." This maximum in 

 the year 1752, and those shown on Prof. Loomis' auroral curve 

 about the years 17S0-90, 1S50, and 1S7Q-72, agree very ill with 

 each other, or wdth the return of a const int cycle of long period 

 connecting them together ; the succession more nearly resembles 

 that of periods of hot summers, or of cold winters, governed by 

 fixed laws that have not yet been discovered in their returns and 

 durations : and seems to point to causes influencing the production 

 of auroras very similar to those which determine some of the 

 obscurest features of our seasons. Thus, since the commencement 

 of the earliest continuous temperature records at the Royal Obser- 

 vatory, Greenwich, in the year 1 77 1, the commencement of winter 

 or the arrival of a mean daily temperature of 40° has fluctuated 

 between the months of November and December, apparently 

 from different degrees of prevalence in those months of an 

 annual tide of south-west wind then reaching a maximum in 

 the British Is'.es. Assuming changes in the strength of this 

 wind to be the cause of the observed fluctuations and of a gradu- 

 ally increasing retardation of winter and secular rise of mean 

 temperature in the months of November, December, and January, 

 noticed by Mr. Glaisher during the first half of the present 

 century, the average course of this phenomenon, when submitted 

 to examination, resembles very closely the general course of tlie 

 curve of auroral frequency. Tliere was a sensible retardation of 

 the winter season from abjut the year 1775 to about the year 

 1790, followed by a marked acceleration from the latter year 

 onwards through nearly the first quarter of the present century, iri- 

 dicating apparently a considerable abatement of south-west, anti- 

 trade, or equatorial currents, on an average, for that lengthened 

 period. The acting cause hiwever returned, and its strength 

 may be gathered from the fact that the mean temperature of the 

 month of December at Greenwich during the twenty-five years 

 from 1825 to 1S50 was higher in eight years than that of the month 

 of November, an anomaly which had only taken place thrice in 

 the first quarter of the century. The last occurrences of the same 

 kind, with which I am acquainted, happened in the years 185S, 

 1861, and 1S62 ; but the strong retardations of winter, noticeable 

 towards the year 1S50, were then rapidly disappeiring, and it is 

 not improbable that m the farther fluctuations that have smce 

 followed, a new correspondence between the secular rise of tem- 

 perature of the months of November, December, and January at 

 Greenwich, and the considerable maximum of auroral intensity 

 reached during the years 1870-1873, may be found to bear out an 

 analogy which is only hazarded here, in the absence of a better 

 working hypothesis, as an apparently real and perhaps not alto- 

 gether unnatural connection, 



With regard to the relative proportion between eastward and 

 westward movements of auroral rays, 1 know of no observations 

 that have been made that can offer Mr. Procter any additional 

 information. The possibility that auroral streamers may be up- 

 rushes of positive or negative electricity to a point of saturation 

 in the highest regions of the atmosphere, followed by down- 

 rushes of the same electricity when the exciting cause in the 

 interior or on the surface of the globe subsides, might be well 

 proved by such observations. The existence of the motion shows 

 that the auroral rays diverge sensibly from the earth's lines of 

 magnetic force, probably in the endeavour (whether effectual or 

 not is indifferent to the explanation) of the Aurora Barealis and 

 Aurora Australis to combine and to neutralise each other (perhaps a 

 rare occurrence) across the equator. The strength of the motion of 

 the beams may be some measure of this tendency, and its absence 

 a sign that the aurora is local and of comparatively little generality 

 and extent. It may here be remarked that the annual periodicity 

 of auroras differs entirely from that observed in the average fre- 

 quency of sporadic shooting stars, which reiches a maximum in 

 August and .September, but has a well-marked minimum in 

 March, resembling the single cold of winter and the single heat 

 of summer produced three months earlier, in each year, by the 

 tropical motion of the sun. A marked frequency of auroras on 

 the dates of January 1-3, April 19-21, August g-ii, October 

 18-21, November I4and27, and December io~i2, when meteor- 

 showers of various degrees of brightness are of almost annual 

 occurrence, has not, as far as I am aware, been definitely traced 

 and established ; but the large auroral catalogues recently pub- 

 lished by Prof. Loomis and Prof. Lovering wdl, it is evident, 

 supply very valuable materials by which any such connection 

 between auroras and periodical meteor-showers, if it exists, can 

 be more thiro'ighly investigated anl determined. 



A. S. IIersciiel 



Automatism of Animals 



Your correspon leu', Mr. Wetterhau, has, I ihin'K, misun- 

 derstood Prof. Huxley's argument ; which is, not that the 

 adjusted motions he refers to never were the result of conscious 

 and voluntary motion, but that they are not so now. His letter 

 has, however, induceil me to call attention to what has always 

 seemed to me a real difficulty. As I understand automa'ic or 

 reflex actions, they are those which have been so constantly 

 repeated and whicli are so essential to the we'1-being of the 

 individual, that the various nerves implicated have become si 

 perfectly co-ordinited that the appropriate stinmlus sets the 

 whole machinery in motion without any conscious or voluntary 

 action on the part of the individual. Thus we can quite under- 

 stand how a paralysed limb would be drawn up when the sole of 

 the foot is tickled or the toe pricked. If, however, any such 

 irritation continues to be felt in the normal state, a min would 

 stoop down and remjve the irritating substance with his hand, 

 or would place his foot upon the opposite knee, and, stooping 

 down, endeavour to sec the object which caused the irri- 

 tation. But these are clviscious, not reflex, acts. They are not 

 repeated often enough, and are not sufficiently identical in form, 

 to become automatic ; and we are not told that a wdioUy para- 

 lysed human body does actually go through these various mo- 

 tions, as it certainly would do if not paralysed. 



Now, in the case of the frog I can quite understand the jump- 

 ing, swallowing, swimming, and even the balancing ; for all 

 these are actions so essential to the animal's existence, and so 

 often repeated during life, as to have become automatic. So, 

 also, I can understand the drawing up of the foDt to remove an 

 irritation on the side of the body, for with the short-necked frog 

 this toj is an essential, and must liave been an oft-repeated 

 action. But we are further told that "if you hold down the 

 limb so that the frog cannot use it, he will, by and by, take 

 the limb of the other side anl turn it across the body, and use it 

 for the same rubbing pro;ess." Now, this seems to me not to be 

 explicable by automatic or reflex action, because it cannot have 

 been an action frec[uently if ever performed during the life of 

 every frog. It is true that from the co-ordination of the move- 

 ments of the opposite limbs, we might expect, if the irritation 

 were continued, and the leg on the same side kept for some time 

 in motion, that the other leg would begin to move in the same 

 way. But what causes it to move in a quite dilTerent and un- 

 usual way, across the body to the opposite side ; and this, as 

 related, at once and without first trying its own side ? The most 

 usual motion of both legs is directly up and down, each on its 

 own side. What is it that causes one of these legs, when it 



