6o6 



NATURE 



[April 2Z, 1 88] 



current machine by removing the commutator, thereby 

 producing a very effective machine. 



All theoretical determinations of the efificiency of 

 machines are complicated by the retardation of mag- 

 netisation of the magnets, which necessitates a change 

 of position of the commutator or brushes in the direction 

 of the rotation of the armature. The practical deter- 

 minations of efficiency which have been made show that 

 from 86 to 88 per cent, of the energy communicated to a 

 dynamo-machine is converted into electrical energy, and 

 that from 44 to about 50 per cent, of the total work may 

 be converted into useful work in the e.xternal circuit. 

 Among the more recent continuous current machines are 

 the Brush and the BUrgin machines, which promise to 

 give good results. 



At intervals during the lecture the room was lighted by 

 various electric lamps, the peculiarities of each of which 

 were explained. The Brockie lamp, lent by the British 

 Electric Light Company, and served by one of their 

 Gramme machines ; the Siemens pendulum-lamp lent by 

 Dr. Siemens, and the Crompton lamp lent by Mr. 

 Crompton, were each tried in turn, and attention was 

 drawn to the Siemens' differential lamp, the Brush lamp, 

 and other lamps and electric candles which were also 

 exhibited. 



_ The subject of the fourth Cantor lecture was the sub- 

 division of the electric current and lighting by incan- 

 descence. Prof. Adams showed that objections raised to 

 the electric light were similar to those which had been 

 urged with regard to gas when it was first introduced. He 

 then compared the energy of Grove's cells with the energy 

 derived from a small Gramme machine, and showed how 

 impracticable it was to attempt to do by means of batteries 

 the work which can be done by such machines. He then 

 explained how the same amount of energy might be 

 spent in two classes of machines, those of low internal 

 resistance and low electromotive force which send a 

 strong current through small external resistance, or 

 quantity machines, and those of high internal resistance 

 and high electromotive force sending a smaller current 

 through large external resistance, or tension-machines. 

 For very high resistinces the discharge of an induction- 

 coil is taken, the action of which was compared to the 

 action of the hydraulic ram. Prof. Adams proceeded to 

 describe the Werdermann and the Joel lamps, and ex- 

 plained the kind of machine specially suited for such 

 lamps, and regretted that it would not be possible to 

 show them to the best advantage, or to give them a fair 

 trial, because the machine actually in use at the speed at 

 which it was running was not adapted for them. An 

 electromotive force of 130 volts will send 50 webers 

 through 10 lamps in series, and give an illumination of 

 320 candles in each lamp for an expenditure about 10 

 h. p. Taking Mr. A. Siemens' facts as to the cost, it 

 appears that the electric light from the Joel lamp would 

 be as cheap as gas at the rate of 2s. per 1000 cubic feet. 

 The laws of the subdivision of the electric current were 

 discussed, and their application to the system of incan- 

 descent lighting adopted by Swan, and by Lane-Fox and 

 Edison was clearly shown. With the Burgin machine, 

 then in use, giving at 1620 revolutions a minute an 

 electromotive force of 160 volts, and a current of 24 

 webers through an e.\ternal resistance of about 7 ohms, it 

 was shown that 24 rows of two Sw^an lamps in series or 

 48 lamps could be lit up : each lamp being of 80 ohms 

 resistance, and giving a 48 candle-power light. If the 

 resistance of each lamp be 40 instead of 80 ohms, then 

 double the number of lamps might be taken in series, 

 giving about- loo lamps from the machine. 



With the Brush machine at least 140 lamps might be 

 lit up in 10 parallel rows of 14 lamps in series. The 

 early attempts of King, and Staite, and Konn to light by 

 incandescence were then explained, and experiments 

 made to illustrate the phenomena seen in high vacua, 



such as are necessary to enable Mr. Swan and Mr. Lane 

 Fox to preserve their carbons from wasting when ren- 

 dered incandescent by means of the electric current. 



The room was well lighted by means of 20 Swan 

 lamps, each giving a pleasant and steady light of about 

 40 or 50 candle-power, the lamps being arranged in 10 

 rows of two in series. Two table-lamps were placed on 

 the lecture- table, which could be put out separately or 

 made to glow at pleasure, and these lamps could be 

 lifted off their stands and others put in their places with, 

 out disturbing other lights which were arranged in mul- 

 tiple arc and worked from the same dynamo-machine. 



THE FRENCH ASSOCIA TION FOR THE 



ADVANCEMENT OF SCIENCE AT ALGIERS^ 



II. 



Algiers, April ij 

 /^N Friday afternoon various papers on local subjects 

 ^^ were read to a general audience in the foyer of 

 the theatre. 'Ihey related to the geology, geography, and 

 demography of Algeria, but the most interesting paper 

 was by our Consul General, Col. Pla_\fair, on a visit to 

 the country of the Kroumirs — interesting not only be- 

 cause the aggressions of this tribe have led to the present 

 complications in Tunis, which will probably end in war, 

 but also because Col. Pla>fair and Lord Kingston are the 

 only Europeans who have visited their country. They 

 inhabit the district near Le Calle, that is to say, the 

 northern portion of the boundary between Algeria and 

 Tunis, and they only nominally acknowledge the suzerainty 

 of the Bey of Tunis. 



On Friday evening a discourse was delivered in the 

 theatre " On Paludisme from a Surgical Point of View." 

 It was of such a very technical character that many 

 members of the Association did not attend. In fact the 

 Congress is to a great extent medical. While the Physical 

 and Botanical Sections are positively languishing for 

 want of papers, and will probably come to a premature 

 ending on Mondaj', the papers waiting to be read before 

 the Medical Section fill two pages of yesterday's pro- 

 gramme. 



Alore activity was manifested in the sectional work on 

 the second day of the Congress ; the papers in most of the 

 sections were more numerous and the audiences larger. 

 The physical section is the most neglected of all. Long 

 after the proper time of commencement the president had 

 not made his appearance, and at length jlr. Siemens, 

 the only honorary vice-president, was requested to tal.e 

 the chair. Of the four papers read three \se.\^ by 

 Englishmen, and on the fiist day of meeting one paper 

 alone was read by a Dutchman. Pure physics in France 

 is unfortunately quite unrepresented at the Congress. 

 In the Chemical Section M. Baunhauer read a paper 

 " (_ n the Crystallisation of the Diamond," and M. de 

 Foreland " On a New Apparatus for Gas Analysis." 

 There were several good papers on meteorological sub- 

 jects. Only three papers were read in the Geological 

 Section, the most important of these by M. V'illanova, 

 "Cn the L'nification of Geological Nomenclature." The 

 Anthropological Section was well attended, and papers 

 of considerable local interest were read. The Sections 

 of Geography and Political Economy mainly discused the 

 Sahara — on the one hand its physical geography, and on 

 the other its colonisation. 



In the Agricultural E.xhibition one of the most in- 

 teresting machines is the solar engine, the boiler of 

 which is placed in the axis of a mirror 14 feet in diameter, 

 and formed of three portions of hollow truncated cones, 

 so as to get a close approximation to the parabola. When 

 the sun shines a pressure of from three to four atmo- 

 spheres is produced in the boiler, and a force of one- 

 horse power is produced through the intervention of an 



* Continued from p. 583. 



