Aug: 5, 1875J 



NATURE 



^n 



quarters of an hour. From the data published by Coum- 

 bary we might infer on the hypothesis of circular' motion, 

 that the body, whatever its nature, had moved at a dis- 

 tance of about 415,000 miles from the sun's surface, and 

 as we know from the experience afforded by the great 

 comet of 1843, there is nothing improbable in a comet 

 having so passed. Perhaps when the sun's disc is more 

 systematically and widely watched, a comet may be caught 

 in transit and properly observed. The case of the comet 

 of 1 8 19 is not a satisfactoiy one, Pastorfif's observation at 

 least attributing to it a position upon the sun's disc which 

 it could not have occupied at the time he assigns to his 

 observation. 



Comet 1874 (II). — The comet detected by M. Coggia 

 at Marseilles on April 17, 1874, which presented so fine 

 an appearance in our northern heavens in July, was 

 observed at Melbourne, and by Mr. Tebbutt, near 

 Sydney, until the end of the first week in October. 

 Comparing the Melbourne observation on the 6th of 

 this month with the place given by the elliptic ele- 

 ments of Prof Tietjen, the difference is found to be less 

 than a minute of arc, and the European observations 

 to the middle of July are very accurately represented by 

 these elements. Between April 17th and October 6th 

 the comet traversed an arc of 205° of true anomaly, and 

 the near agreement of Prof. Tietjen's orbit throughout, 

 shows that the comet when it attracted so much attention 

 was really moving in an ellipse of very long period, 

 though no doubt this element may be considerably varied 

 without largely increasing the differences between calcu- 

 lation and observation. The period of revolution in 

 Tietjen's ellipse is nearly 9,000 years. When a similar 

 complete investigation has been made for this comet to 

 that so skilfully performed by Dr. von Asten in the case 

 of Donati's great comet of 1858, some kind of limits may 

 be assigned to the time of revolution, but in all proba- 

 bility it must extend to some thousands of years. We 

 remark that the Melbourne observations of Coggia's 

 comet were made with a telescope of only \\ inches aper- 

 ture ; no doubt the comet might have been followed some 

 time longer with larger instruments, but it is possible 

 that the Melbourne reflector may have been under pre- 

 paration for the transit of Venus, and not conveniently 

 available for cometary observations. 



PROF. LOO MIS ON THE U.S. WEATHER 

 MAPS* 



THIS paper is in continuation of a similar paper pub- 

 lished in July last year, in which the American 

 Weather Maps for 1872-73 were discussed. The results 

 then arrived at are compared with the observations of 

 1874, and the whole is thereafter combined into a three 

 years' average. 



The principal conclusions from the three years' obser- 

 vations are these : — 



The mean direction of the onward course of stormi is 

 N. 81° E., or a little to the north of east, being most 

 southerly in July (E. 7° S.), and most northerly in April 

 and October (N. 72° E. and N. 74° E.). The mean 

 velocity is 26 miles per hour — the maximum monthly 

 velocity, 32 miles, being in February, and the minimum 

 i8'4 miles in August. As regards particular storms, wide 

 deviations from these figures take place, it being found 

 that the actual motion of the storm's centre may have a 

 path in any direction whatever, and the velocity of pro- 

 gress may vary from 15 miles per hour towards the west, 

 to 60 miles per hour towards the east. From the tri- 

 daily observations it is found that the average velocity of 

 storms from 4*35 P.M. to 11 P.M. is about 25 per cent, 

 greater than for the rest of the day, and that while this 



• Results derived from an examination of the United States Weather 

 Maps for 1872-7^-74. By Prof. Elias Loomis, Yale College. P'rom the 

 American jfournal of Science and Arts, vol. x.j^uly 1875. 



varies in different months from 14 to 32 per cent., the 

 most rapid progress occurs in every month during this 

 portion of the day. Prof Loomis suggests that as this is 

 the time of the day when the temperature is falling most 

 rapidly, the fall of rain may be thereby accelerated, and 

 the velocity of the storms' progress be increased by the 

 more rapid extension of the rain-area which would follow. 

 The meteorological system of the States fortunately 

 furnishes the required data for the examination of this im^ 

 portant point, and we shall look forward with great 

 interest to discussions of the daily rainfall of the States in 

 this connection. 



It would appear that an unusual extension of the rain- 

 area of a storm is generally accompanied by a velocity 

 of progress greater than the mean. The average extent 

 of the rain-area eastward from the centre of the storm is 

 542 miles ; but when the eastern extent of this area is 100 

 miles greater than the mean, the hourly velocity of the 

 storm's progress is increased 13I miles ; and when on the 

 other hand, the eastern extent of the rain-area is 100 

 miles less than the mean, the hourly velocity of progress 

 is diminished gi miles. Whilst the extent of the rain- 

 area exercises an important influence on the storm's pro- 

 gress, the inclination of its axis would also appear to 

 influence to some extent the course of the storm. Pro- 

 fessor Loomis is of opinion that the direction and velocity 

 of the storm's progress may be predicted with some con- 

 fidence, in cases when the precise limits of the rain-area 

 are known. It is thus most desirable that rain observa- 

 tions form an integrant part of all weather telegrams. 



The influence of areas of high barometer on the 

 velocity and direction of a storm's course is important in 

 connection with the prediction and theory of storms, but 

 further observations are required for its elucidation, 

 among the more important of which are the movements 

 of the upper currents of the atmosphere as disclosed by 

 observations of the cirrus cloud. 



The reports of General Myer, Chief Signal Officer, for 

 1872-73-74 show by the barometric results for Denver and 

 the other elevated stations on the spurs of the Rocky 

 Mountains, that the relative distribution of atmospheric 

 pressure at these great heights is just the reverse in sum- 

 mer and winter of what obtains at lower levels to east- 

 ward in these respective seasons. The point is a vitally im- 

 portant one in its bearings on the weather and meteorology 

 of the States. In connection with it, we have examined with 

 much interest the tables at pp. 10 and 1 1 which give the 

 number of times during 1873 and 1874 on which the daily 

 change of temperature amounted at the different stations 

 to 40° and upwards. This large temperature fluctuation 

 occurs most frequently at Colorado Springs, Denver, and 

 the other high stations in the west. The most remarkable 

 of these changes occured at Denver on the 14th of 

 January 1875, at which place the temperature was below 

 zero all day, and the wind N.E. At 9 p M., the tempera- 

 ture was i°.o and the wind suddenly shifted to S.W. ; at 

 9.15 P.M., the temperature had risen to 20°. o at 9.20 p.m. 

 to 27°.o ; at 9.30 p.m., to 36°.o ; and at 9.35 P.M., to 40°.o, 

 after which there was little change till the following morn- 

 ing. At 11.30 A.M. of the 15th, the temperature was 

 52°.o and at this time the wind suddenly backed to N.E. ; 

 at 12.30 P.M., the temperature had fallen to 4°.o Thus in 

 the evening of the 14th, the temperature rose 39°.o at 

 Denver in the short space of 35 minutes, and about 

 noon of the following day fell 48°. o in one hour. 



ON THE HORIZONTAL PHOTOGRAPHIC 

 TELESCOPE OF LONG FOCUS* 



IN what I have now to say in regard to the methods 

 of Photography employed in observing the recent 

 Transit of Venus, I shall confine myself to the subject of 



* This paper was read by the late Prof. Wenlock to a private scientific 

 Club in Cambridge, U.S., shortljpbefore his death ; it has been forwarded 

 to us for publication, at the request of the Club, by Prof. Asa Gray. 



