6i6 



NATURE 



{Oct. lo, 1878 



Intra- Mercurial Planets 



The places sent you of the objects which I designated by {a) 

 and {b) in my observations during the total eclipse on July 29 

 were derived from the hurried readings of the circles made im- 

 mediately upon my return from the Eclipse Expedition, in order 

 to be able to answer numerous inquiries addressed to me for 

 information in regard to these observations. Subsequently I 

 made a careful determination, and the readings of the circles 

 and all the data for a definitive reduction of the observations 

 were communicated to astronomers in this country and in 

 Europe. These have probably already come to your know- 

 ledge and need not be repeated here. 



The only outstanding question in regard to the place of the 

 star which I designated by {b), is whether any disturbance of the 

 telescope by the wind is to be feared. The position was marked 

 on the hour circle first, and but a moment was occupied in 

 passing from the eye-piece to the place where this was done. 

 The wind was blowing fresh from a direction south of west, but 

 our telescopes were, as yon ,know, well sheltered by the semi- 

 circular ledge behind which we observed. My own instrument 

 -was near the ledge on the west, and was more completely pro- 

 tected than any of the others, and hence it became desirable to 

 Jcnow whether any such disturbance of their instruments was 

 noticed by Prof. Newcomb, Commander Sampson, and Lieut. 

 Bowman, who observed near me. Accordingly, I addressed 

 letters to these gentlemen for information upon this point. Prof. 

 Newcomb read the circles of his instrument for a pointing made 

 at about the same instant, which proved to be on a fixed star, 

 and there was no disturbance whatever of the position of his 

 telescope, Lieut. Bowman says that there was no disturbance 

 of his instrument by the wind during the totality, and Com- 

 maiader Sampson says that his assistant, Dr. Dewitt, who pointed 

 for him while using the spectroscope, did not notice any 

 disturbance. 



These reports might be regarded as conclusive upon the ques- 

 tion which I raised, when I came to reduce the observations, 

 since otherwise the star {b) could not be ^ Cancri. If the totality 

 had only lasted a few seconds longer I might have moved out to 

 f Cancri, and by observing it also there would have been no 

 uncertainty whatever. But I hardly realised at the time the 

 possibility of there being two planets near the sun, and being 

 sure of one, I gave more attention to it. The record of {b) was 

 made just before the sun reappeared. In fact, the sun came out 

 just as I turned to go to the eye-piece again, and anxious to have 

 Prof. Newcomb's telescope also directed on (a), I ran across to 

 where he was observing, but his telescope being then directed 

 toward a suspicious object, for which he was reading the circles, 

 it could not be disturbed. Returning to my own instrument it 

 was too late to re-observe {b) or to find ^ Cancri, and I could 

 not then determine whether the object observed was a stranger 

 or not. It was very much brighter than I expected to see 

 J,' Cancri, judging from the appearance of S Cancii, which I had 

 seen in. a preceding sweep. 



In order to obtain further evidence as to the stability of the 

 I'nstrument, I have made careful experiments with it, clamped as 

 it was then, and I find that the danger feared has no significance 

 whatever. During the present week, also, there have been days 

 when the wind was blowing very strong from the same direction 

 as on the day of the eclipse, and I have placed the telescope in 

 the position as to direction in which it then was, but fully 

 exposed to the wind, and it has remained hours at a time thus 

 exposed without the pointing being sensibly changed. I 

 conclude, therefore, that the object which I designated by (/') 

 is also a new star. 



. I. have lately examined, on two mornings, the stars in that 

 jjartof Cancer, and my recollection of the appearance of the 

 stars (a) and (p) being still vivid, I have compared, with the 

 same telescope and magnifying power, the stars which I then 

 observed in the vicinity of the sun. The moon shining brightly 

 in the west, and the' bright twilight in the east, gave a sky- 

 illumination in some respects similar to that at the totality of the 

 eclipse. By observing when the approaching daylight had 

 extinguished the, light of two small stars which I saw on July 29 

 cast. of the sun, so that they were just visible in the telescope as 

 they were on that day,. I proceeded to compare the light of 

 Q and ^ Cancri. As a. result of this examination, I am convinced 

 that I underrestimcfted the magnitudes at the time. I think that 

 (a) must be classed as good fom-th magnitude, and {b) as third 

 iaaghitude, if not brighter. James C. Watson 



P.S. — I have begun some calculations, but being pressed just 



now in the preparation of elements, perturbations, and epheme- 

 rides of ten or twelve of the minor planets for the Berliner 

 Astr. yahrbuchf I have not yet progressed very far. It is 

 probable that M. Gaillot will have worked up all the material 

 available for this, J. C. W. 



Ann Arbor, September 21 



Sun-spots and Weather 



In the last number of Nature (p, 567) there is a very inte- 

 resting communication from Mr. Fred. Chambers of Bombay. 

 He shows that the barometric pressure at Bombay when gra- 

 phically exhibited for a series of years, gives a curve which is 

 ^•ery similar to the sun-spot curve, and he remarks that the baro- 

 metric curve lags behind the sun-spot curve particularly in the 

 years of maximum sun-spots. He argues that the sun is probably 

 hottest at times of maximum suu'spots. I have grounds for 

 thinking that I found traces of a somewhat similar relation in 

 discussing the daily range of the thermometer at Kew Observa- 

 tory, although the results obtained were not so definite as those 

 of Mr. Fred. Chambers. 



When, however, we go from the meteorological to tlie mag- 

 netical influences of the sun we find a very marked and well- 

 known relation between the sun-spot areas and the magnitude of 

 the diurnal range of declination — this diiurnal range being unmis- 

 takably greater wlien there are most spots. Here also the 

 lagging behind comes prominently out whatever may be its 

 cause. 



Mr. Frederick Chambers quotes the following remark made 

 by me (Nature, vol. xvii, p. 326) : — 



" It is nearly, if not absolutely, impossible from observations 

 already made, to tell whether the sun be hotter or colder as a 

 whole when there are most spots on his surface. The sooner we 

 get to know this the better for our problem." 



I ought here to mention that in these words I referred more 

 particularly to direct observations of the heating effect of our 

 luminary. I ought also to state that the fundamental importance 

 of such observations was impressed ujxjn me by the remarks of 

 a very distinguished physicist, who considers that a persistent 

 and well -organised attempt should be made to determine by 

 means of actinometric observations whether our lurainary is in 

 reality of variable heating power. 



We know a good deal about sun-spots, although not nearly so 

 much as we ought, but we know next to nothing about the 

 variations (if any) in the direct heating effect of the sun. I can 

 only here repeat what I said before, that "the sooner we get to 

 know this the better for our problem." Balfour Stewart 



Manchester, September 27 



Cyclones and the Winter Gales of Europe 



The following figures may interest some of your readers as a 

 contribution to the theory put forward in Nature, vol. xvi. 

 p. 505, regarding the meteorological effects of variations in the 

 intensity of solar radiation, and of the consequent changes in 

 terrestrial temperature. 



According to this theory, the high temperature which gene- 

 rally coincides with sun-spot minima should have the effect of 

 increasing the steadiness and velocity of the prevailing winds of 

 the globe, whilst, at the opposite epoch of the solar cycle, the 

 weakness and unsteadiness of these currents ought to give rise to 

 heavy rain on the coasts and islands of the tropics, and to 

 facilitate the generation of cyclones, which (as has been shown 

 by Messrs. Blanford and Eliot in the case of the Bay of Bengal), 

 are most probably caused by the condensation of aqueous vapour 

 over the place of its production. If this view of the action 01 

 variations in temperature upon the convection currents of the 

 atmosphere be the true one, it follows that the south-westerly 

 gales of Europe should be most frequent and powerful at times 

 when the cyclones of the West Indies are least frequent. This 

 is borne out by the accompanying table, ^-hich shows the 

 number of hours in each year during which the wind-velocity in 

 the British Isles exceeded thirty miles, as compared with the 

 number of cyclones in the West Indies, according to Poey, 

 The figures in the second line are taken from the Quarterly 

 Weather Reports, and represent the averages of the annual 

 totals for Valencia, Armagh, Glasgow, Aberdeen, Sandwick, 

 Falmouth, Stpnyhurst, and Kew. These are the only stations 

 which give a continuous register for the six years in the table. 



