7 04 



NA TURL 



[May 31, 1883 



and the sun across the sea. One of your correspondents lias 

 suggested a more probable origin, viz. particles of ice in the air. 

 From other correspondents it seems that the sun column is not 

 always vertical, which might be ihe result of the general flame 

 of the reflecting surface not being parallel with the earths 

 surface. 



In the June number of the Philosophical Magazine there was a 

 notice of a sun column as seen at Orkney by the Rev. C. Clouston, 

 who at that period made meteorological observations for that 

 publication. He says that in the month of April of that year 

 the drought was unprecedented, the atmospheric pressure great, 

 and the temperature high. I believe two of these character- 

 i tics belonged to the recent month of April if not the third, 

 the high temperature. He says it was seen six timas and once 

 or twice before he noted the date, and also before sunri-e 



Saltlmrn, May 21 E. R- Turner 



Sheet Lightning 



May not this be an auroral phenomenon, at times, at least, 

 and hence the differences of opinion as t 1 its nature? Reading 

 Wilkes's "Narrative of the U.S. Expedition," I find the fol- 

 1 owing :— " On the 7th February (1840) the weather hid become 

 less boisterous, and having reached latitude 49° S., longitude 

 (55°-23 E., the aurora Australis again appeared. It was first 

 seen in the north, and gradually spread its coruscations over the 

 whole heavens ; the rays and beams of light radiating from ne lrly 

 all points of the horizon to the zenith, when their distinctive out- 

 lines were lost in a bright glo* of light, which was encircled by 

 successive flashes, resembling those of heal lightning on a summer's 

 night. The-e formed a luminous arc in the southern sky, about 

 2t? ill altitude, from the upper part of which rays were c .11- 

 tinually flashing towards the zenith. Light showers of rain 

 finally shut it nut from view." Fred. Pratt 



Clapton Park, May 25 



Pocky Clouds 



For twenty years I was constantly observing the forms and 

 appearances of the clouds, as clues to the weather and its changes. 

 1 observed this form on a very great number of occasions, and 

 from experience always --ame to the conclusion, "no rain to- 

 day," and I can only remember two occasions on which the con- 

 clu-ion was not justified. I saw it again a few d.iys ago, with 

 the same result of good weather. 



I always termed it the "huible" cloud till I saw Dr. 

 Clouston's work. It seems to me to be a body of vapour the 

 upper surface of which is being acted upon by an upper current 

 of very dry and rarefied air, causing a great and rapid evapora- 

 tion, and thence a gradual and unequal cooling anl shrink ige of 

 the under surface in the de ached globules from which it takes its 

 name. I hive seen a very simple illustration while passing 

 ihrough the laundry, and observing a neglected trough of soap- 

 ^ds cooling d >wn and nucleating in the exact form presented by 

 the pocky cloud, and with the same gradations of tint. 



This kind of cloud is generally observable at periods most 

 probable for storms and electric condensations, the which, acting 

 at a distance, would influence outlying areas of upper atmo- 

 sphere and cause this form of cloud con lensation in the way ex- 

 plained. In my observations I have generally found the cloud 

 revert to uniform sheet stratus rather than to disappear in cloud- 

 lets in the upper air. Fred. Trait 



Clapton Park, May 25 



Clerk Maxwell's "Devil on Two Sticks" 

 In the very interesting life of Clerk Maxwell which has lately 

 appeared there are frequent references to a philosophical toy, 

 from which he seemed to derive endless amusement. He calls 

 it the "devil on two sticks." Can you give your readers any 

 account of it ? The editors take it for granted that the appara- 

 tus is well known, but I cannot find any one here who can tell 

 me what it is. Denny Lane 



72, South Mall, Cork 



The Centres of a Triangle 



Continuing my suggestion in your number of May 3 (p. 7), 

 I propose not only to call the circle circumscribing a triangle the 

 circumcircle, but also to call its centre the circumcentre, and in 

 the same way to speak of the incentre, the three excentres 



(namely, the <;-excentre, the A-excciltr™ and the r-ex:e.itre), and 

 the inidccntre. 



The line joining the circumcentre to the orthocenire, on which 

 the misscentre and the mi"! centre lie, may b; appropriately 

 called the central line of the triangle. 



Similar abbreviations would apply to the radii of these circles ; 

 they might be spoken of as the circum radius, the imadius, the 

 a-cxra litis, the bexradius, the c exradius, and the midradius. 



May 25 W. II. H. II. 



THE ROYAL GEOGRAPHICAL SOCIETY 



THE annual meeting of the Royal Geographical 

 So:iety on Monday was of rather more than 

 usual scientific interest. Sir Joseph Hooker was pre- 

 sented with the Royal Medal which the Society has 

 awarded him, Mr. Colborne Baber being the recipient of 

 the Patron's Melal; while among the speakers at the 

 dinner, besides Sir Joseph Hooker, were Mr. Spottiswoode 

 and Prof. Huxley. From the address of the President, 

 Lord Aberdare, it is evident that geographical research, 

 and especially exploration, has been as active as ever 

 during the past year, yet, as the speakers we have named 

 pointed out, the discovery of new countries must have a 

 limit, and in time must come to an end. Still there will 

 be plenty of work for geographers to do in the wider 

 acceptation of the term geography, implied in the presen- 

 tation of the Royal Medal to so distinguished a botanist 

 as Sir Joseph Hooker. In the words of Mr. Spottis- 

 woode, and as we have frequently pointed out in these 

 pages, geography in its modern acceptation includes "an 

 accurate delineation of the earth's surface, and an exact 

 account of its inhabitants and of their habits, of the 

 animal and vegetable life, and its distribution over the 

 face of the globe." In this direction the Society has a 

 long and brilliant career before it But as Prof. Huxley 

 humorously pointed out in replying for the "other societies," 

 these societies " were all growing a little dull. He did not 

 say this in the way of reproach. The progress made in 

 research and accuracy in methods of procedure involved 

 that consequence. So long as there were large regions of 

 knowledge which the methods of modern science had 

 not penetrated, so long was it possible to go to meetings 

 of societies, and to hold brilliant discussions. Looking 

 at the means which now existed for the diffusion of infor- 

 mation, he had been led to think that in many cases 

 where the field of knowledge had been extensively ex- 

 plored the utility of societies was constantly diminishing, 

 and that sooner or later it would be necessary to devise 

 other means of effecting the results now attained by 

 meetings of societies. But there was one thing which would 

 not be reached at any period of time by any other organisa- 

 tion than that of societies, and that was the stimulus which 

 was given by their meetings to investigators ; and the 

 reward they found for their toils and sacrifices in such a 

 welcome as had been given that night to his long-tried 

 friend Sir J. Hooker." 



The prosperity of the society continues to be maintained. 



Mr. Clements' Markham read the annual report, which 

 showed that during the year the number of Fellows elected 

 was 163, besides three honorary corresponding members, 

 and the total number of Fellows on the list (exclusive of 

 honorary members) was 3392. The total net income for 

 the financial >ear ending December 31, 1SS2 (exclusive of 

 balance in hand and 1005/. sale of Exchequer Bills) was 

 7937/., of which 5652/. consisted of entrance fees and 

 subscriptions. The net expenditure during the past year 

 was 8779/., including 1 1 3 5 A spent on expeditions. The 

 sale of 1000/. of Exchequer Bills was rendered necessary 

 to meet the Society's contribution to the Eira Relief 

 Expedition, but this sum had since been generously pre- 

 sented to the Society by Mr. Leigh Smith. The invest- 

 ments and assets of the Society on December 31, 1882, 

 exclusive of the map collection and library, amounted to 

 39.83". 



