^:a6 



NA TURE 



{March 23, 1876 



dyne. I use vis (pi. vires') to express the absolute unit of force in 

 the F. P.S. system of units, with the multiples decemvires, cen- 

 iivires, millivires. Thus nine centivires is very closely equal to 

 the weight of twenty- eight pounds in this country. 



I should add that the distinction between "weight" and 

 "mass," generally recognised, but not uniformly insisted on in 

 practice, is clearly pointed out in Prof. Everett's useful tables. 



University Hall, March i8 J.J. Walker 



The Dry River-beds of the Riviera 



Those who have visited the Riviera of Piedmont will re- 

 member as one of its most remarkable features the broad stony 

 river-beds, sometimes with a meagre rill trickling down a narrow 

 channel in the middle, sometimes entirely dry, but never with any 

 body of water sufficient to account for the immense bed ; the 

 Paglione at Nice, with its bed spanned by a bridge of three 

 broad arches, and with a stream never more than four or five 

 feet wide and a few inches deep, is a specimen of what I mean. 

 Can any of yoar scientific readers tell me what and when was 

 the change of climate which caused what must once have been 

 large rivers to shrink into mere rivulets? To all appearance it 

 must have been within historical times, as the river-beds are dis- 

 tinct and still bare, without any encroachment of vegetation. 

 Probably the simplest way of accounting for the phenomenon 

 would be, by showing that there has been a great diminu- 

 tion in the snow lying on the Alpes Maritimes, which are 

 drained by these rivers. It is remarkable, too, that in many of 

 the narrow valleys running up into the hills, now quite dry, 

 there are evident traces of torrents and waterfalls apparently in 

 recent times. R. E. Bartlett 



Nice, March 7 



The Ocelli in Insects 



At vol. xlii, p. 168, H. Miiller calls the attention of entomolo- 

 gists to a subject which has interested other entomologists be- 

 fore — the function of the ocelli in insects. With due deference to 

 a suggestion made by such an authority, it seems to me that the 

 size of the ocelli in hymenopterous insects is not dependent on 

 their nocturnal habits. Why in hymenoptera more than in other 

 orders ? Indeed, it may be doubted whether in some insects 

 the ocelli are organs of vision at all, or at least whether they are 

 of any practical use as such in the imago. Their number, as 

 well as size, differs in different species of the same, order, seem- 

 ingly without regard to their habits, whether diurnal or nocturnal, 

 and in many moths they are so completely concealed by the 

 scales that it is necessary to divide the head to ascertain whether 

 they are present or absent, so that it is dif&cult to understand 

 ho\v they can be of any service as organs of vision. May they 

 not in the imago, in such cases, be merely functional remnants of 

 larval organisations. C. 



Colorado, Feb. 15 



The Recent Storm 



Your meteorological readers will probably guess that I have 

 made an error of an inch inadvertently in the barometer readings 

 of Sunday week. Also the last line should contain " nme 

 hours " in place of seven. T. S. UsBORNE 



Staplehurst, Kent, March 21 



OUR ASTRONOMICAL COLUMN 



Struve's Companion of Procyon.— Mr. Otto Struve, 

 in his remarks at the Royal Astronomical Society, iu 

 May, 1874, upon the later Pulkowa observations of the 

 faint companion to Procyon, which he discovered on 

 March 19, 1873, and which has been supposed to account 

 for the anomalous motion of the latter, established by 

 the researches of Prof. Auwers, referred to the circum- 

 stance of the small star not having been up to that time 

 perceived with the 26-inch refractor of the Washington 

 Observatory. Admiral Davis, the present superintendent 

 of this establishment, has communicated to the Astrofio- 

 mische Nachrichten, the particulars of observations prin- 

 cipally instituted for the purpose of confirming the exist- 

 ence of Struve's companion. The observations were 

 commenced in November 1873, and have been continued 



to the beginning of the present year. On no single occa- 

 sion have Professors Newcomb and Holden, the usual 

 observers, or any one who has examined the star with 

 the 26-inch refractor, been able to detect a companion in 

 the position assigned by the Pulkowa measures. Close 

 faint stars have, however, been remarked in other position- 

 angles, about three of which it is stated no doubt is 

 entertained : — 



1. Position about 10° ... Distance 6" 



2. „ ... 36' •.• „ 8"-8 



3. „ about 50* ... „ less than 10" 



And it is said to be quite possible there may be one or 

 two more. No. 2 is the most readily visible. 



Mr. O. Struve's measures gave the following mean 

 results : — 



1873, March 28 ... Position 9o"'-24 "... Distance i2"-49 



1874, April lo ... „ 99° -60 . „ ii"-67 

 How then is the contradictory character of the PulkoAa 



and Washington observations to be accounted for ? It 

 can hardly be, as suggested by Mr. Struve, that "the 

 surpassing brilliancy of the principal star may have 

 hindered the recognition of the small companion in its 

 neighbourhood," since notwithstanding it does not appear 

 that a smaller aperture than 22 inches was employed 

 during the Washington observations, three closer com- 

 panions were considered to be certainly in existence. 

 There remains the supposition of variabihty of light of 

 the Pulkowa companion, if difiference of atmospheric cir- 

 cumstances be ignored as inadequate to explain the want 

 of success of other observers in detecting it. 



Nothing more is heard of the Smythian orange- tinned 

 eighth magnitude distant from Procyon in 1833, 145''' on 

 an angle of 85°. As is well known, the only observation 

 confirmatory of the existence of this star is that by Mr. 

 Isaac Fletcher, M.P., early in March, 1850, which gave 

 for the position 84° 19' ; most unfortunately the distance 

 was not measured, because there is a star of similar 

 brightness on very nearly the same angle but at a distance 

 of about 330" measured by Capt. Jacob, Mr. Powell, and 

 the late Lord Wrottesley. Anyone, however, who reads 

 Mr. Fletcher's letter to Admiral Smyth, printed in 

 " Sidereal Chromatics," p. 69, will see that there is little 

 doubt the object observed in 1850 was the same that 

 was measured, or rather estimated, as to position in 

 1833, the difiference of distance not admitting of a mis- 

 take on the part of an experienced and careful astro- 

 meter. The more distant star was judged to be blue by 

 Mr. Powell ; the orange-tinge recorded in " the Cycle " is 

 a characteristic of a large number of the known variable 

 stars. 



The Total Solar Eclipse of 1883, May 6.— -In this 

 eclipse, in which the duration of totality where the sun is 

 near the meridian will exceed five minutes, the course of 

 the central line appears to be a most unfavourable one 

 for observation, being almost eatirely a sea-track. The 

 elements are very approximately as follows : — 



Conjunction in R.A., May 6, at 9h. 44m. 42s. G. M.T. 



R.A 43° 30' 52" 



Moon's hourly motion in R. A 38 23 



Sun's „ „ „ 2 25 



Moon's declination ... ... ... 16 II 32 N. 



Sun's „ 16 37 53 N. 



Moon's hoarly motion in decl. ... ... 7 26 N. 



Sun's „ „ ,, o 42 N. 



Moon's horizontal parallax ... ... 60 52 



Sun's „ „ o 9 



Moon's true semi-diameter ... ... 16 35 



Sun's ,, „ 15 51 



Hence the central and total eclipse begins upon the earth 

 in longitude 156° i' E. of Greenwich, and latitude 34° 43' S., 

 and ends in longitude 86" 44' W., and latitude 13^ 41' S. ; 

 the eclipse is central with the sun on the meridian in 

 147° 4' W., and 9° 1 1' S. The following are also points 

 upon the central line : — 



