March 8, 1894] 



NA TURE 



441 



has for its contents the first part of a memoir by Dr. Max 

 Thiesen, entitled " Kilogrammes Prototypes." The paper con- 

 tains the results of comparisons of the weights of forty-two 

 standard kilograms, designated Prototypes nationaux, made by 

 Dr. Thiesen between 1886 and 1888. Of the 251 comparisons 

 made, 230 were executed according to the scheme adopted by 

 the International Committee of Weights and Measures in 1886; 

 the remaining 20 had for their object the determination of the 

 influence of transport on the prototypes. The plan of observ- 

 ation and all the elements used in the reduction of the observ- 

 ations are included in the present paper ; but the details of the 

 investigation, and the discussion of the results, are reserved for 

 a future volume. 



The astronomical observations made by Tobias Mayer, at 

 Gottingen, from 1756 to 1761, were published in 1826 by the 

 Commissioners of Longitude. Five years later, Baily's memoir 

 on Mayer's catalogue appeared, together with a comparison of 

 the places of most of the stars with those given by Bradley. The 

 celebrated " Sternvergeichniss " has again been discussed, this 

 time by Dr. A. Auwers, with the assistance of other astronomers, 

 and the results are given in a volume published by Engelmann, 

 of Leipzig. The catalogue thus produced contains the places of 

 1027 stars computed for the epoch 1755.0. The volume also 

 includes a discussion of Mayer's positions with those given by 

 Bradley and others for the same epoch, a good series of proper 

 motions being obtained by the comparison. 



In these democratic days, very few journals affect to ignore 

 the requirements of that undefinable quantity — the general 

 public. This is what Science Pi ogress does, however, in its 

 first number, a copy of which has been sent to us. All the 

 articles in this new publication are what our friends across the 

 Channel term articles de poids — solid dissertations on the pre- 

 sent state of knowledge of various subjects. Prof Fitzgerald 

 contributes a suggestive article on physical science and its con- 

 nections, and Mr. J. W. Rodger describes the new theory of 

 solutions founded by van't Hoff. Insular floras are passed in 

 review by Mr. W. B. Hemsley, and the importance of the study 

 of fossil plants is made out by Mr. A. C. Seward. The origin 

 and nature of certain bacterial poisons forms the subject of an 

 article by Dr. G. A. Buckmaster ; the present outlook of verte- 

 brate morphology is discussed by Prof. G. B. Howes, and a 

 summary of the most important papers recently published in 

 chemical physiology, or physiological chemistry, is given by 

 Prof. W. D. Halliburton. Such are the subjects dealt with in 

 the new magazine. References lie on the pages as thickly as 

 leaves in Vallambrosa, and show the immense amount of work 

 that has been done. The new venture appears to stand in the 

 same relation to the majority of scientific journals as the heavy 

 monthlies do to weekly newspapers. We hope that it will meet 

 with a large measure of success. 



In a recent number of Eleciricitt' {Vax'is), M. G. Claude gives 

 an account of some experiments he has made on the electric 

 arc in an alternating circuit. The phenomena produced by 

 the disruptive discharge, in spite of the numerous experiments 

 made with a view to elucidate them, are still far from com. 

 pletely elucidated. Thus, for example, it is well known what 

 lengthy discussions have taken place over the question whether 

 the electric arc, either with a continuous or alternating current, 

 is the seat of a back electromotive force, or whether it behaves 

 simply as an ordinary metallic resistance ; yet it would be hardly 

 true to say that this point has been definitely settled. In one 

 of his experiments M. Claude joins two points, between which 

 there is an alternating difference of potential of 2400 volts 

 (frequency about 80 per second), by about 12 incandescent 

 lamps (16 candle-power, 100 volt), a condenser of O'l micro- 

 farad capacity, and a make and break key all placed in series. 

 When the key is closed, the circuit is traversed by the charge 

 NO. I 27 I. VOL. 49] 



and discharge currents of the condenser, the magnitude of 

 which can easily be calculated, and which suffices to make the 

 filaments of the incandescent lamps just glow. If now the key 

 is opened so that there exists a small spark gap in the circuit 

 (about I mm.), an arc will be struck at this point. Now this 

 arc is certainly an additional resistance in the circuit, small it 

 may be, since it is formed between metal points, but which 

 certainly cannot be less than that which existed when the metal 

 points were in contact. It is now found that the lamps show 

 an increased brilliancy, and this brilliancy increases as the 

 arc is made longer. This increase is such that, for the longest 

 arc obtainable (a little over i mm.), the difference in potential 

 between the terminals of each lamp rises from 30 volts to 90 

 volts, while the difference of potential between the terminals 

 of the key is found to be about 1200 volts. The author 

 gives the following explanation of this experiment : — The arc 

 is a discontinuous phenomenon, and requires a certain minimum 

 value to start, and thus, while the E. M.F. is below this value, no 

 current passes, and the condenser remains uncharged. When 

 the limiting E.M.F. is reached, the arc is struck, and the con- 

 denser is charged suddenly at a high potential. This 

 charging of the condenser is limited to a fraction of the com- 

 plete period, so that the charge current lasts a shorter time, and is 

 of greater intensity than when no arc exists in the circuit. The 

 absorption of energy in the lamps being proportional to the 

 square of the current is increased, for the mean square of 

 the current in the circuit is increased when the arc is present. 

 The material forming the points between which the arc is 

 struck, exerts an important influence on the facility with which 

 the arc is maintained when the difference of potential diminishes, 

 so that, although a much longer arc can be obtained by using 

 carbon terminals, the above effect is not nearly so well marked 

 as with terminals of iron or copper. It is of course necessary 

 to have a condenser placed in the circuit to obtain the increased 

 brilliancy of the lamps, for otherwise during the time the spark 

 is unable to pass no current passes, while when the current does 

 pass it has the same value it would have at the same part of 

 the cycle if the spark gap were closed. On performing the 

 experiment, M. Claude finds that when there is no condenser 

 in circuit the luminosity of the lamps is slightly reduced when 

 the arc is formed. 



Mr. A. GiBB Maitland, of the Queensland Geological 

 Survey, points out that the sentences after that beginning "For 

 a general colony map," in Nature, vol. xlix. p. 109 (November 

 30, 1893), refer to the work being carried out by the staff on the 

 Charters Towers Gold-field, and not to the whole colony. 



The additions to the Zoological Society's Gardens during 

 the past week include an Indian Kliie {Miivus govinda) irom 

 India, a Common Kestrel {Tinmmculiis alandarius), a Golden 

 Eagle {Aquila dirysivtus), a Barn Owl {Strix flammea), a 

 Tawny Owl {Syrnitan ahuo) British, a Great Eagle Owl {Bubo 

 maximtis) European, a Spotted Eagle Owl {Bubo maculosa) 

 from South Africa, presented by the Crystal Palace Company ; 

 two Levaillant's Francolins {Francolinus levaillanti), two Barn 

 Owls {Strix flamniea) from Port Elizabeth, South Africa, pre- 

 sented by Mr. B. Matcham ; a Bar-tailed Godwit {Limosa 

 lapponica), a Grey Plover {Squatarola helvetica), a Dunlin 

 {Tringa alpina) British, two Ceylonese Hanging Parrakeets 

 {Loriculus asiaticus) from Ceylon, purchased ; and Eland 

 ( Oreas canna, ? ) born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 

 The Aurora of February 28. — A fine auroral display was 

 observed in various parts of England on the evening of Wed- 

 nesday, February 28. Several letters describing the phenomenon 

 have been received, and the following from Mr. C. Thwaites 

 gives a clear account of the general appearance at Norwich : — 



