Makcii 1, 1001.1 



KNOWLEDGE. 



07 



1 foot height. It was considered that the errors of 

 height due to tho aneroid were never more than 2 to 



Table VI. 



Observations on the Ai'tritlnhc. 



Number!! 

 reoorvleU in 

 the Log. I 



>t;UO of S<>rt. 



Hoisht of Waves 

 in Foct. 



Tr^s-grosse nier 

 Grosse mer 

 Tivsgrossc lioulo 

 Grande lioule 

 Iloule 



Petite houle 

 Belle mer 

 II pr unie 



28-5-t 



20 67 



loi2 



10-83 



7'85 



■1-92 



3-28 



197 



Compare with eolunins 1 and "i of J'lilile IF. 



2.5 feet. The greatest source of eiror in the opinion 

 of the observer occun-ed in the estimation of the height 

 of the eye above sea level. For instance, he says, when 

 the aneroid was at its lowest point the surface of the 

 water might be 10 feet below the eye; but when the 

 crest of the wave was passing, the height might 

 be I'educed to 1 or 2 feet. Here the observer had lo 

 trust to estimation by the eye aided by a few i-ough 

 measiu'ements with a piece of string down the ship's side, 

 end tho error here, he considers, may be at least 2 feet 

 either way, or 4 feet in all. Observations for length 

 and speed were taken in much the same way as those of 

 Paris, witli the advantage, howevei', of a flyback chrono- 

 graph over an ordinai-y seconds hand watch. Aber- 

 cromby mentions two difficulties in obtaining good 

 results, viz., that two successive waves rarely ran in 

 exactly the same direction, and that, with a heavy 

 following sea the ship yawed' about so nuieh that 

 the angle between her course and that of the waves 

 could only be estimated approximately. Really big 

 waves were met with on only 3 days. On June 8th, 

 1885, in lat. 47° S., long. 175° W., the sea was too 

 irregular to measure individual wave heights or lengths, 

 but the barometer indicated about 12.5 feet vertical 

 motion of the point of observation below decks. The 

 surface of the sea was pretty constantly about 7 feet 

 below the porHiole in the troughs, and 1 foot at the 

 crests. This gives an average height of the waves 

 18.5 feet. The velocitv of the waves was pretty constant, 

 although the length appeai-ed to be so irregulai", five 

 observations giving speeds of 29, 28, 31, 33 and 30 miles 

 per hour (average 30.2 miles). On June 10th, in lat. 

 51° S., long. 160° W., the observer availing himself of 

 the previous determination, assumed a constant dif- 

 ference of six feet between the height of the aneroid 

 above water level at crest and trough, and added this 

 to the observed variation of the aneroid. Individual 

 waves were observed with heights of 26, 21, 23.5 and 

 26 feet, but the indication of the aneroid indicated that 

 the difference of absolute level between the lowest trough 

 and the highest crest (not one of those recorded above) 

 was 35 feet. I suppose the inference from this to be 

 that the difference, if a real one, was due to the presence 

 of a long swell susceptible but not visible in tho rough 

 sea, and I apprehend that the revelation of such invisible 

 but not negligible waves is one of the special advantages 

 of the aneroid over eye observation. The velocity and 

 length of waves was meastired just before the heights 

 were taken ; three determinations gave the following 

 residts : — • 



Velocity. 

 32 iuilo9 poi' liour. 

 3.-, 

 39-5 

 285 



Lonirtli. 

 507 foot. 

 ■170 ,» 



3.-,S „ 



Velocity. 

 35'5 miles ppv hour. 

 35-5 



-l-"-5 



This sea, Abercromby says, would Iiavc been logged 

 as 6 or 7 on the ordinary scale of — 8, while tho wind 

 was blowing a moderate to hard gale from N.Vv''. v.-ilii 

 heavy squalls, and was logged 7 on Beaufort's scale of 

 — 12. During some of the squalls the force rose to 8 ; tlic 

 sea, he says, might be taken as a fair average in the South 

 Pacific, the waves were far too irregular to allow of any 

 attempt being made to determine the ratio of height 

 to length or velocity. On July 16th, 1885, lat. 

 55° S., long. 105° W., larger waves were observed 

 during which the greatest vertical lift of the aneroid 

 in tho cabin was luidoubtcdly 40 feet. If tho difference 

 of water level outside was again 6 feet the height of 

 the waves was 46 feet, but of this the obsei-\'cr, who 

 confined his attention to the aneroid, was not sure. 

 Tlio mo.Tsurcd velocities and lenijths were : — 



I.eiia-th. 

 H5 feet 

 48.-1 „ 

 7(i5 „ 



The author states that the want of harmony botwcon 

 the length and velocity on the one hand, and tho height 

 on the other, was not duo to errors of observation. On 

 all the days tho waves were running irregularly ; ho did 

 not see any crests nearly a mile long chasing one anotlier 

 with a well defined trough between. There was nothing 

 to call a cross sea, but there were many scries of waves 

 of different lengths manning pretty much in tho same 

 direction which were constantly interfering with one 

 another. He generalises from his experience (which it 

 must be mentioned were by no means confined to the 

 voyage of which he here speaks) in the statement that 

 the great discrepancies in the observed elements of 

 waves given by different observers is doubtless duo to 

 the co-existence of several series of undulations, which, 

 tlierefore, always make a more or less confused sea. 



The author concludes with suggestions for a wave- 

 measuring party, which he says should be composed of 

 tlu-ee members. A, B. and C. C would have charge of 

 two chronographs, and B of the aneroid. They would 

 confine their attention to reading the instruments, whilst 

 A only would watch the sea. He would observe the 

 arrival and passage of the wave crests, the height of the 

 water against the ship (by marks on the side) at crest and 

 trough, and ho might have to read a simple clinometer 

 also to allow for the roll of the ship. 

 (To he continued.) 



CONSTELLATION STUDIES. 



By E. Walter Maunder, f.r.a.s. 

 III.— THE REGION OF VIRGO. 

 TuE Great Bear still holds the zenith at midnight 

 throughout the month of March, but by the middle of the 

 month the Lion has ceased to be the dominant constel- 

 lation in the south. Its place is taken by the Virgin, 

 which seems almost to lie below the royal beast, for at 

 this time of the year tho ecliptic curves downwards more 

 sharply than at any other period, for its descending node 

 lies close to the boundary of Leo and Virgo and just 

 within the latter constellation. Virgo, therefore, is 

 easily found when Leo is known, or the old rhyming 

 direction will plainly point it out ; — 



