Pre. 2, 1875] 



NATURE 



93 



a; parently to zero, or in reality as I have said to that of the 



atmosphere. 



In the apparatus as here arranged, consisting of the discharging 

 and the recipient cistern, with the intervening jet-orifice and 

 recipient-orifice, the overflow of the recipient cistern is at 18 

 inches above the centre of the orifices. 



As I continue to fill the discharge cistern, you observe the jet 

 shoots across the open space between the orifices, and the water- 

 level continues to rise in the recipient cistern ; and so long as 

 the head in the former is maintained at a moderate height above 

 that in the latter, the whole of the stream enters the recipient 

 orifice, and there is no waste except the small sprinkling which 

 is occasioned by inexactness ot aim, and by the want of exact 

 circularity in the orifices. 



When the; head in the recipient has reached the overflow, and 

 thus remains at a steady height of 18 inches above the orifices, the 

 complete reception is insured by maintaining a head of 2oi inches 

 in the discharging cistern, or an excess of head of 2\ inches on 

 the discharge side ; and this excess, in effect, represents the 

 energy wasted in friction. 



You observe that as I diminish the supply of water and allow 

 the excess of head in the discharger to become reduced, a steadily 

 increasing waste becomes established between the orifices ; and 

 it is interesting to trace exactly the manner in which the friction 

 operates to produce this result. 



Fig. 25. 



If the conoids of discharge and reception are tolerably short as 

 .:hey are here, it is the outer annule or envelopes of the stream 

 which are in the first instance affected, that is to say retarded, 

 yj friction, and the escape or waste between the orifices implies 

 hat this surface-retardation has reduced the velocity of those 

 envelopes below that due to the head in the recipient ; thus an 

 annular counter-current is able to establish itself, and in fact 

 constitutes a counter discharge from the recipient, 

 i As the quantity of water which actually enters the recipient, 

 )r in other words the speed of the inflow, is reduced, the 

 "riction which belongs to that part of the stream is reduced also, 

 JUt that which belongs to the issuing jet is unabated, and this 

 nrcumstance virtually magnifies the waste ; it is probable, how- 

 ;ver, that to the last the velocity of the central zones of the jet 

 emains equal to that due to the head in the discharger, and 

 aence you will observe that unless this is reduced below the level 

 jf the overflow, the head in the recipient is fully maintained to 

 hat level, though the whole quantity discharged is wasted 

 between the orifices. 



When the supply is altogether cut off, both cisterns simul- 

 aneously empty themselves, the two jets meeting between the 

 orifices, and becoming spread into a beautiful plane disc or 

 ilm of water at right-angles to the line of discharge ; but you 

 Jvill notice that from some inequality in the commencement of 

 he action, and to some extent probably from a quasi-instability 

 n the equilibrium of the double discharge, one of the jets will 

 presently for a moment get the better of the other and drive it 

 5ack so as almost to arrest its flow, and thus for the moment 

 irrest also the waste of head on that side ; but the momentary 

 ixcess of head thus occasioned almost instantly asserts its supe- 

 lority, producing a jet of superior force, and thus driving back 

 or a moment the opponent by which it had just before been 

 i.astered. Thus a curious oscillation of discharge ensues, which 

 jS to a large extent a true dynamic phenomenon somewhat ana- 

 '<^ous to that which becomes established in an inverted syphon 

 ^)artly filled with water, if for a moment the head is increased in one 

 >f the legs ; the reaction which in the syphon is furnished by its 

 ;ontinumg through the bend, is, in the case before you, furnished 

 7 the dynamic reaction of the jets, but the circumstances here 



involve an instabiUty which does not exist there, so that the 

 small initial disturbance presently magnifies itself into one of 

 considerably greater range. 



This airious corollary phenomenon of the alternated retar- 

 dation of discharge, though not strictly relevant to the main 

 object of the experiment, is nevertheless highly interesting in 

 itself and tends to enlarge our apprehension of some of the 

 characteristic featiu-es of fluid dynamics. 

 {To be contintud.') 



NOTES 

 Tuesday being St. Andrew's Day, the anniversary meeting 

 of the Royal Society, as required by their charter, was held. 

 The President, Dr. Hooker, began his address with a few 

 remarks on the large number of eminent Fellows whose names 

 appeared in the death-list of the past year, and then gave a 

 i summary of the numerous measures for " the improvement of 

 I natural knowledge" undertaken by the Society. These com- 

 I prise the publication of papers in the " Philosophical Transac- 

 ; tions," in a separate form ; preparation of additional volumes of 

 the catalogue of scientific papers ; the labours of committees in 

 connection with the Transit of Venus Expedition, and the 

 researches ot naturalists in Kerguelen and Rodrigues ; the 

 Eclipse of the Sun Expedition to Siam, the Polar Expedition, 

 the voyage of the Challenger, and of the Committees appointed 

 to consider the suggested modification of the regulations under 

 which candidates are elected into the Society. The auditors' 

 report showed that the pecuniary resources of the Society were 

 in a satisfactory condition, and Dr. Hooker mentioned the 

 bequests made to the Society by the late Sir C. Wheatstone and 

 Mr. H. Dircks. The medals were then presented, the Copley 

 medal to Dr. Hofmann, a Royal medal to Mr. Crookes, and a 

 Royal medal to Dr. Oldham (at present in India), through Prof. 

 Ramsay. The proceedings terminated with the election of 

 council and officers (comprising the list of names already pub- 

 lished) for the ensuing year. We hope to refer at length next 

 week to the President's address. The anniversary dinner was held 

 at W' illis's Rooms, Dr. Hooker in the chair, supported by the 

 Marquis of Salisbury, Lord Cardwell, Mr. W. H. Smith (of the 

 Treasury), the Right Hon. Robert Lowe, Mr. Farrer, Admiral 

 R. Hall, Mr. Lyon Playfair, Dr. Hofmann, Mr. Crookes, and 

 a large number of the Fellows of the Society and their friends. 



On Monday night there was a pleasant and lively meeting at 

 the Royal Geographical Society, over Mr. Stanley's work on the 

 Victoria Nyanza. The paper read was by Col. Grant, C.B., 

 the old companion of Speke, and he awarded hearty praise to 

 Stanley, whose work he estimated as of high geographical im- 

 portance. At the same time he showed that Stanley's dis- 

 coveries seemed to confirm the discoveries of Speke as far as 

 these went. The former estimates the circumference of the lake 

 at 890 geographical miles, which coincides essentially with 

 Speke's estimates. Sir Samuel Baker spoke much to the same 

 effect as Col. Grant, both as regards Stanley and Speke, as did 

 also Capt. Burton, while Mr. Edwin Arnold acted the part of 

 Stanley's representative. It was announced that the Church 

 Missionary Society are to take advantage of King Mtesa's invita- 

 tion to send out missionaries ; Sir Samuel Baker believes that the 

 good Mtesa mistook Stanley for Livingstone, whom he had been 

 informed might be expected from the south. Sir H. Rawlinson 

 read some extracts from Col. Gordon's letter on the Albert 

 Nyanza, which he trusted would also be explored by Mr. 

 Stanley. 



The Queen has conferred upon Dr. W. B. Carpenter, F.R.S., 

 the honour of the Companionship of the Civil Division of the 

 Order of the Bath. 



The Royal Academy of Sciences of Berlin has elected 

 Dr. Frankland and Prof, A. W. Williamson, of London, cor- 

 responding members of the section of Physics and Mathematics. 



