61- Royal Institution of Great Britain. 



variable star in the constellation Serpens, mentioned in No. 5. of 

 the Society's monthly notices. (See Phil. Mag. N. S. vol. ii p. 226.) 

 He says, it is now again become visible, and has already attained the 

 8th or 9th magnitude. Its position for the beginning of this year is 



M = 15" 46 m 45 s Decl. = + 15° 39' 30" 

 and he invites astronomers to watch this star during the period of 

 its changes. 



A communication was then read from Mr. Rumker of the obser- 

 vatory at Paramatta in New South Wales, giving an account of his 

 observations for determining the absolute length of the pendulum 

 vibrating seconds there, according to Borda's method. The ap- 

 paratus, with which these experiments were made, was constructed 

 by Fortin, of Paris, and taken out to the colony by Sir Thomas 

 Brisbane. There are some slight alterations from the apparatus 

 described by M. Biot, which are pointed out by Mr. Rumker : and 

 he also alludes to a new method of observing the coincidences. In 

 Borda's method, the coincidence is determined by the intersection 

 of the wire of the pendulum of experiment with a cross marked on 

 the bob of the pendulum of the clock. In lieu of this cross, Mr. 

 Rumker placed a small graduated arc, and the determination of the 

 coincidence resolves itself into observing the moment when the wire 

 describes its minimum amplitude on the arc. Mr. Rumker likewise 

 adopts a new mode of determining the correction for the arc of vi- 

 bration. He finds that in large arcs (such as 8 or 9 degrees, to 

 which his arcs sometimes extend) the decrease is not in a geome- 

 trical progression, when the times are in arithmetical progression. 

 He has therefore formed a table of the actual decrease of the arcs 

 as observed by himself, at equal intervals of five minutes each ; and 

 given the corresponding corrections for each interval. In the course 

 of his reductions he notices some errors in the formula given by 

 M. Biot for finding the centre of oscillation of a pendulum con- 

 structed according to the method of Borda. The mean of 41 series 

 of experiments gives the length of the pendulum, vibrating seconds 

 at Paramatta, in vacuo, at the freezing point, and at the level of the 

 sea, equal to 992-412801 millimetres, or 39-071618 English inches. 



PROCEEDINGS AT THE FRIDAY-EVENING MEETINGS OF THE 

 ROYAL INSTITUTION OF GREAT BRITAIN. 



May 23. — Mr. Brockedon on a new method of projecting shot. 

 — This method belongs to Mr. Sievier. It consists in making the shot 

 with a cylindrical chamber, so as to pass freely on to a maundril or 

 bar fixed on trunnions, a powder-chamber being formed at the bottom 

 of the cylindrical cavity in the shot. The powder is inflamed by 

 means of a touch-hole in the shot, in the usual way. A charge of 

 powder thus used is found to produce effects very much surpassing 

 that occasioned when a shot of equal weight is thrown from a can- 

 non ; and this is accounted for by supposing that the force, of recoil, 

 which in a cannon is so great as to throw it a considerable distance 



backwards, 



