466 



NATURE 



[April 11, 1878 



The "Eurydice" Squall 



The loss of H.M.S. Eurydice on the 24th ult, may perhaps 

 give a melancholy interest to a plain statement of the facts con- 

 nected with the meteorology of that day. 



The squall in which she capsized was one of a common class 

 which occur when, after a long steady fall of the barometer, the 

 mercury pauses for a few hours before commencing to rise. 

 These squalls differ considerably from simple squalls, and are 

 frequently complicated, as in this case, with small secondary 

 cyclones. 



Since the 20th inst. the general type of weather over our 

 islands had been very uniform, an area of high pressure being 

 constantly found over the west of Ireland, with a constantly low 

 pressure near Stockholm giving cold north-west winds, conditions 

 which are very common in the month of March. But while the 

 general shape of the isobaric lines remained constant, the abso- 

 lute pressure over the whole area had been diminishing rapidly 

 till the 24th inst. On the morning of that day, the centre of a 

 cyclone was near Stockholm, while no less than three secondary 

 depressions were influencing Great Britain, and by 6 P.M. the 

 whole system had gathered itself into two small cyclones whose 

 centres were near Yarmouth and Bergen. 



Such a development of secondaries with a north-west wind is not 

 common, and is always associated with exceptionally wild and 

 broken weather, of the kind which gives heavy local rainfall, 

 with squalls, or violent cold thunderstorms, but not widespread 

 or destructive gales. 



In London the changes above described were well shown by a 

 steady fall of the barometer from the 21st inst., which amounted 

 to an inch at 3. 45 P.M. on the 24th. As a heavy squall came 

 on then, the barometer jumped up suddenly two-hundredths of an 

 inch, as is often the case in squalls, and then fell slowly in about 

 a quarter of an hour to its former level, where it remained sta- 

 tionary till about 9 P.M., after which it rose steadily. The 

 squall, which lasted about twenty minutes, was followed by 

 veiy threatening-looking weather, during which the wind per- 

 haps backed a little to west-north-west, but at 4.40 p.m. it 

 shifted to north-north-east and became strong, with heavy snow, 

 till 5.20, when the weather moderated, the whole being evi- 

 dently due to the complicated action of one of the secondary 

 depressions before mentioned. 



Materials are still wanting for tracing the connection between 

 the squall in London at 3.45 P.M., and that at Ventnor at the 

 same hour, but squalls often do occur simultaneously at distant 

 places in connection with the trough of great non-cyclonic baro- 

 metric depressions. The c^uestion of any such relation has not 

 yet been worked out, and its solution presents great difficulties. 



On the whole, then, the squall in which the Eurydice was lost, 

 though of a common type, was somewhat exceptional in sudden- 

 ness and violence. Ralph Abercromby 



21, Chapel Street, S.W., April 3 



Leidenfrost's Phenomenon 



A FEW days ago I was examining the " rosette " formed by a 

 spheroid of water in a hot platinum capsule, and noticed that 

 the outline was not a continuous curve, as is generally represented 

 in books, but was " beaded " with re-entering angles as shown by 

 the continuous, lines in figures Aj, B3, C3, whUe the curve of 



A9? 



each bead could be distinctly traced within the drop, forming a 

 "fluted" outline, shown by the dotted lines in the same figures. 

 It was at once manifest that both the "beaded "and "fluted" 

 figures were produced by the superposition of the retinal images 

 of the drop in two extreme conditions of vibration ; that, 

 in the case represented by A3, the drop was really vibrat- 

 ing like a bell which is sounding its first harmonic above 

 its fundamental note, and therefore possesses six ventral 

 segments, the extreme forms assumed being represented by 



Aj and A2 respectively, and that B3 and C3 represent the 

 appearance of the drop when vibrating like a bell which 

 is sounding its second and third harmonic respectively. To 

 verify this a spheroid of about five-eighihs of an inch in diame- 

 ter was produced ; and as soon as the beaded decagon, C3, was 

 steadily maintained, the room was darkened, and the spheroid 

 illuminated by sparks from Holtz's machine. Immediately the 

 curvilmear pentagons c^ and Cg were apparent, and frequently 

 the vibrations continued perfectly steady for several seconds. 

 When the drop had diminished in size the mode of vibration 

 changed, and the crosses represented by B^ and Bg appeared when 

 the sparks passed ; on opening the shutters the beaded octagon b, 

 appeared almost perfectly steady in the capsule. The figures A^, 

 Ag, and A3 were obtained in the same manner, and with a larger 

 spheroid twelve and sixteen beads were obtained, presenting 

 respectively curvilinear hexagons and octagons when illuminated 

 by the sparks. In one case a small spheroid presented a very 

 large number of beads in its outline ; but on examining it with 

 sparks it was found to be produced by the crosses Bj and b, 

 rotatmg very rapidly about a vertical axis. Two or three par- 

 ticles ot carbon introduced into a spheroid remained for a long 

 time close to the surface of one " ventral segment," like lycopo- 

 dium powder on a Chladni's plate, and when they escaped from 

 it were ensnared by the next segment. The figures observed 

 when the spheroids were illuminated by sparks' were fully as 

 exorbitant as those shown at A^, Aj, Bj, b^, Cj, and Cg. 



If the spheroidal form be due to the combined action of 

 gravity and surface tension, it is obviously to the latter force that 

 we must look for the production of vibrations when, by any 

 accident, the spheroid is disturbed. The amount of steam 

 produced from the under-side of any " ventral segment " will, 

 of course, be greater the greater the surface exposed ; and when 

 this is a fresh surface, will increase as the surlace becomes heated 

 by exposure. Hence the amount of steam escaping from beneath 

 a "ventral segment" will be greater as it is contracting towards, 

 than when it is moving from, the centre of the spheroid, thus 

 supplymg, on the whole, during each vibration an impulse in the 

 direction of motion. It seems unnecessary to look farther for a 

 supply of energy. Wm. Garnett 



Cavendish Laboratory, Cambridge, March 15 



Trajectories of Shot 



Having observed a letter in Nature, vol. xvii. p. 401, in 

 which extracts from a paper of mine are commented upon by the 

 Rev. F. Bashforth, I trust you will let me make a few remarks 

 by way of explanation. 



In the paper referred to ,1 was trying to weigh against one 

 another the merits of different methods of finding the trajectories 

 of shot, the calculations being, of course, based upon Mr. Bash- 

 forth s tables ; and the method which I liked the best did not 

 contain the equation (a), which is the text of Mr. Bashforth's 

 letter. Now without doubt the method I preferred had faults of 

 Its own, but it was a sort of argument in its favour if I could 

 show that the other methods were not faultless, and in particular 

 if I could show that the equation (a), which is the key of those 

 other methods, had no merits of severe accuracy to set off against 

 certain defects which I thought it might fairly be charged with. 



The objections I had to the equation (a) are parUy set forth in 

 the first extract quoted by Mr. Bashforth ; but one great objec- 

 tion to it is the tediousness of its application in practice. Mr 

 Bashforth appears to be greatly offended with my description of 

 the way the equation is used, viz., that it is a process of guessing. 

 But he cannot pretend that he has solved the equation according 

 to any strict method ; he has only guessed at a solution which 

 falls in more or less with his tables. It seems to me he is here 

 quarrelling about a mere name, because the process he describes 

 and indeed illustrates is practically the process I describe, and it 

 is idle on his part to give me the information contained in his 

 letter, because I am very well aware that the second guess gives 

 a better result than the first. But as regards the amount of 

 accuracy belonging to the equation, I must still hold by the 

 substance and tendency of my remarks on that subject, except 

 in my unfortunate use of the epithet "dangerous," which I 

 admit was extreme. I frankly confess that the force of the 



argument derived from discussing the values of ^' is materially 



weakened when these values are numerically exhibited and com- 

 pared with the tables. At the same time, when taken in con- 

 nection with the peculiar way the equation is used, the numbers 



