570 



NA rURE 



[April 14, 1S92 



1891. 



April 16 



„ 18 



., 19 



» 20 



>• 21 



Decl. 



21 44 50 ... +8 21*2 



21 48 13 •• 9 •6"5 



21 51 35 ... 10 ii'i 



21 54 55 ... II 4-9 



21 58 13 ... II 57-8 



22 I 30 ... 12 499 

 „ 22 ... 22 4 45 ■•• 13 41'2 



,, 23 ... 22 7 59 ... 14 31 6 



Displacement of Radiant Points. — The late Dr. J. 

 Kleiher left behind him a paper "On the Displacement of the 

 Apparent Radiant Points of Meteor Showers due to the Attrac- 

 tion, Rotation, and Orbital Motion of the Earth." The paper 

 appears in the March number o{ Monthly Notices of the R.A.S. 

 The three principal causes of di.splacement mentioned in the 

 title are treated separately, and the theory is illustrated by a 

 consideration of the Perseid and Andromedid radiants. More 

 than twenty years ago Schiaparelli developed formulas for 

 determining the amount of displacement of a radiant point due 

 to the attraction of the earth. The efifect of the attraction is to 

 diminish the zenith-distance of every radiant and leave its azimuth 

 unchanged. The corrections to be applied to the co-ordinates of 

 the Peiseid and Andromedid. radiants on account of this dis- 

 turbing cause were computed by Dr. Kleiber, and are given in 

 his paper. It is shown that the latter swarm affords a good 

 example of the displacement of a radiant due to the attraction 

 of our planet. The rotation of the earth produces a small 

 aberration of radiants, never amounting to more than i° in 

 the latitude of Greenwich. With regard to the earth's orbital 

 motion, Dr. Kleiber found that it is sufficient to explain the 

 displacement of 57° in right ascension, and 10" in declination, 

 observed by Mr. Denning in the case of the Perseid swarm. 

 And, after the proper corrections have been applied, it appears 

 that of the forty-nine radiants catalogued by Mr. Denning as 

 belonging to the Perseid shower, "forty-six lie within a circle 

 described about the cometary radiant with a radius of 2°." 

 This important result settles definitely the question as to the 

 reality of the shift of radiant points. 



Two New Variables in Cepheus. — Mr. Paul S. Yendell, 

 in the Astronomical Journal, No. 258, communicates the dis- 

 covery of two variabiles of long period in Cepheus. One of them, 

 D. M. 50° 2769, has a range of variation of a full magnitude 

 (5'8 mag. to 6'8 mag.) in about a year. An interesting point 

 is that "the star is apparently subject, especially near its 

 maxima, to sudden and considerable fluctuations in light, often 

 amounting to several steps from one night to the next." The 

 star No. 8594 of Chandler's " List of Stars probably Variable " 

 has been proved to be variable. The period is about 348 days, 

 and the light-range about 07 mag., from 6"2 mag. to 6'9 mag. 



On the Variation in Latitude.— At the Paris Academy 

 on March 28, M. Faye said : — " The question of the variability of 

 latitudes has lately occupied the minds of astronomers and 

 geodetists to a large extent. The Academy will hear with 

 interest that this question appears to be settled in the affirmative 

 by some observations that the Geodetical Association has re- 

 cently had made at Honolulu. Whilst at Berlin, Prague, and 

 Strasliurg, the latitude increased o""04 from June to September, 

 and afterwards decreased o""i or o"'2 to December, and then 

 diminished o"'i3 to January, at Honolulu it varied in the 

 opposite direction— that is, it fell about o"'3 from June to 

 September, and increased o"'i3 from December to January." 



THE INSTITUTION OF NAVAL ARCHITECTS. 



T^HE annual spring meeting of the Institution of Naval 

 -'■ Architects was held on Wednesday, Thursday, and Friday 

 of last week, the President, the Earl of Ravensworth, occupying 

 the chair during the whole of the sittings excepting that of 

 Thursday evening, when Admiral Sir John Hay presided. The 

 programme was not quite so long as usual, the Council of the 

 Institution having come to the conclusion — wisely, we think — 

 that it would be more desirable to have fewer papers and devote 

 more time to their respective consid- ration. As it is now settled 

 that the Institution is always to hold two meetings in the year, 

 there is a chance of relief to what was always a congested pro- 

 gramme when the business of the whole year was crowded into 

 a single session. Where the summer meeting is to be held this 

 year is not yet settled, but it is to be hoped that some place in 



the provinces will be selected, as it is right that the great ship- 

 building centres of the Kingdom, of which London is not one, 

 should be visited by the leading shipbuilding institution. 



The following is a list of the papers read, in the order in which 

 they were taken : — On divisional water-tight bulkheads as 

 applied to steamers and sailing-vessels, by B. Martell, Chief 

 Surveyor Lloyd's Register of Shipping ; on steadying vessels at 

 sea, by J. I. Thornycroft ; notes on some recent experiences 

 with H.M. ships, by W. H. White, C.B., F.R.S. ; a ram 

 vessel and the importance of rams in war, by Commander E. B. 

 Boyle, R.N. ; whale-back steamers, by F. C. Goodall ; on an 

 approximate rule for the vertical position of the centre of 

 buoyancy, by S. W. F. Morrish ; on balancing marine engines 

 and the vibration of vessels, by A. F. Yarrow ; some notes 

 on the strength of steamers, by A. Denny ; on the trans- 

 verse stability of ships, and a rapid method of determining it, 

 by W. Hok; notes on experiments with inflammable and ex- 

 plosive atmospheres of petroleum vapour, by J. H. Heck ; on 

 the theoretical effect of the race rotation on screw propeller 

 efficiency, by R. E. Froude ; performance of three sets of 

 engines belonging to the second-class cruisers recently added to 

 H.M. Navy, as calculated from the full-power steam trials, by 

 Mr. J. G. Liversidge, R.N. 



It is evident that the space at our command will not permit 

 us to give anything approaching a full description of a meeting 

 that occupied five sittings, some of them of over four hours' 

 duration ; and we will therefore concentrate our attention upon 

 those points more especially within our scope. Mr. Martell's 

 paper was one of great value, but it was treated from a purely 

 constructive point of view. There are, it may be remarked in 

 passing, some very nice mathematical and physical considera- 

 tions involved in the study of the theory of bulkheads. This 

 was pointed out by Dr. Elgar during the discussion, but up to 

 the. present we are not aware that the matter has been ap- 

 proached in a philosophic spirit. Before that can be done, 

 certain experimental data must be obtained, and it will then 

 remain for the mathematician to apply the canons of his 

 science to the elucidation of the problems involved. 



Mr. Thornycroft's paper on the steadying of vessels at sea was 

 an account of some investigations and experiments carried out 

 by one of our most scientific and careful mechanical engineers. 

 Mr. Thornycroft has a steam-yacht, the Cecile, of 230 tons 

 displacement. With this vessel he proceeded to make experi- 

 ments with a view to reducing the rolling motion in a sea-way. 

 The Cecile, it should be stated, is a bad roller, or, rather, a 

 difficult vessel to prevent from rolling, as she has larg<* meta- 

 centric height and a flat floor ; in other words, she has consider- 

 able stability. In this vessel Mr. Thornycroft fitted, under 

 the cabin floor, a shaft, which was free to turn completely round 

 its axis, and to this was keyed a mass of ballast weighing 

 8 tons. The shaft had a crank, which was actuated by an 

 hydraulic motor. In this way the ballast could be moved out 

 from the centre line of the ship, so as to counteract the rolling 

 motion. The movement of the weight had naturally to be 

 provided for by some automatic arrangement, and this was sup- 

 plied by a short-period pendulum placed near the centre of 

 gravity of the ship, and actuating the valves of the motor. So 

 far, all is simple enough, but here the difficulties commence. 

 The inertia of the heavy mass of ballast will cause some loss of 

 time, as only a limited force could be used for its control, and 

 Mr. Thornycroft sets himself the task of overcoming this 

 difficulty. He therefore introduced a second pendulum, of 

 long period, which tends to move the ballast in an opposite 

 direction to the first pendulum, and this enables the apparatus 

 to discriminate between the angular motion of the water and 

 that of the vessel. Mr. Thornycroft found, however, that the 

 long-period pendulum is rather a delicate instrument, and its 

 function can best be served by a cataract arranged to always 

 slowly return the ballast to the centre. This device has the 

 effect of accelerating the phase of motion, which in some cases 

 is required. Unfortunately, at this point Mr. Thornycroft's 

 description breaks off. The mechanism by which the motion 

 of the pendulum is made to govern the movement of 

 the weight was described by Mr. Beauchamp Tower, 

 who has seen it in operation, as " the greatest intel- 

 lectual treat to all who appreciated the niceties of 

 mechanical design." This intellectual treat was denied to 

 the members of the Institution, for the mechanism was not 

 described further than that it was an electrical device. Those, 

 I however, who have attemptea to work with pendulums on board 



NO II 7 2, VOL. 45] 



