90 



NATURE 



[May 26, 1892 



after doing much good work, but Sir William MacGregor has 

 been very active in opening up British New Guinea. 



Reference was also made to the progress of the hydro- 

 graphic surveys in different parts of the world. 



In the evening the anniversary dinner of the Society took place 

 at the Whitehall Rooms, Hotel Metropole, and was attended by 

 a large gathering of Fellows, with many of the leading scientific 

 men and members of the Diplomatic Service as guests. The 

 President occupied the chair. A clever speech was delivered by 

 Mr. Whymper, in response to the toast of " The Medallists. 

 Mr. Bryce, Colonel Maurice, Prof. Flower, Mr. W, T. Thiselton 

 Dyer, and Mr. Norman Lockyer responded to the toast of " The 

 Allied Sciences and Sister Departments." 



TRANSFORMERS} 

 A LTHOUGH transformers are in constant use for changing 

 alternating currents of electricity from high to low or 

 from low to high potential, exact calculations concerning them 

 have hitherto been looked upon by scientific men as impossible 

 because of the complicated law of magnetization which must 

 subsist in iron. Calculations on the assumption of constant 

 magnetic permeability were thought to be worthless, therefore, 

 although these were the only ones which could be made. 

 Certain graphical methods of representing what occurred were, 

 however, based upon the constant permeability hypothesis, 

 and although such graphical methods could only be useful in 

 illustrative work, they were thought to be accurate enough when 

 great accuracy was impossible. The absence of a theory was 

 supplied by vague statements regarding the effects of hysteresis ; 

 and the cycle of magnetization being supposed to be exactly the 

 same, however rapidly performed, and Foucault currents being 

 ignored, it was possible for any writer to get hi* literature on 

 this subject published and read and commented upon. 



Prof. Perry has for a long time preached the doctrine that 

 the only theory of the transformer that can be carefully worked 

 out — namely, that in which hysteresis is ignored — ought to be 

 worked out and compared with experimental results ; and he 

 insisted that when the known phenomena of magnetic leakage 

 and slight saturation and Foucault currents are taken into 

 account, the results of this theory explain all observed experi- 

 mental results. 



In the present paper he takes up the general case of a trans- 

 former with many primary and secondary circuits with magnetic 

 leakage, Foucault currents, choking coils and condensers in 

 series with or in parallel to any or all the circuits. He clears 

 away much of the old difficulty by proving that, in all calcula- 

 tions except that of the idle current supplied to an unloaded 

 transformer, in all practical cases, exactly the same answers are 

 obtained, to four significant figures or more, whether we assume 

 the most complicated of hysteresis cycles or whether we assume 

 the very simplest, which is that of constant permeability. It is, 

 for example, interesting to observe that a formula never hitherto 

 published as correct, often enough used by manufacturers as 

 sufficiently correct for practical purposes, is really a very correct 

 formula. It is also shown that the mathematical difficulties 

 introduced by condensers and magnetic leakage efface themselves 

 completely now that the complete problem has been attacked, 

 and that the numerical working out of the most complicated 

 cases is a very simple matter. 



The one problem on transformers in which it is necessary to 

 consider the law of magnetization of the iron — namely, the calcu- 

 lation of the idle current when the transformer is unloaded — is 

 solved by the author in general terms, and he gives a simpler 

 solution, which in his opinion agrees with all experimental 

 results, although it assumes that there is no hysteresis in the 

 iron. 



SCIENTIFIC SERIALS. 



The only important paper in the Nuovo Giornale Botanico 

 Italiano for April is an elaborate one by Signor G. Paoletti on the 

 movements of the leaves of Porlieria hygromelrica. The 

 structure of the plant is described in detail, and especially the 

 anatomy of the " motor nodes " of the leaves and of the leaflets. 

 He distinguishes in them two kinds of tissue, a motor system 

 and a passive system. The cause of the movements appears to 



1 Abstract of a paper read at the Royal Society, May 12, -by Prof. 

 Perry, D.Sc, F.R.S. 



reside in the protoplasm and in the osmotic properties of the 



I cell-sap. The author is unable to find in the leaves any hygro- 



j metric properties, the supposed presence of which was the reason 



for the specific name of the plant. The paper is illustrated by 



four plates. 



The greater number of the papers in the 2nd, 3rd, and 4th 

 numbers of the Bullettino della Societa Botanica Italiana for 

 1892 are chiefly of local interest to Italian botanists. Among 

 those of a wider scope are the following : — Signor L. Macchiati 

 describes an appearance presented by Navicula elHptica, which 

 he considers strongly to confirm Castracane's view of the 

 occasional reproduction of diatoms by internal germs. — Signor P. 

 Pichi gives the results of experiments on the power of the vine 

 to absorp sulphate of copper through the roots as a specific 

 against the attacks of Peronospora. Analysis of the ash showed 

 the presence of copper in leaves taken from both the upper 

 and the lower branches. — Signor L. Piccioli gives some details 

 respecting the destruction of plants by different kinds of land 

 and freshwater snails, with the amount which is devoured of 

 different plants. This is generally greater in the spring than in 

 the summer. 



In the Botanical Gazette for April, Mr. G. E. Stone describes 

 and figures a self-registering auxanometer, which can be readily 

 consti'ucted, of much simpler construction than those at present 

 in use in botanical laboratories. — Mr. Conway Macmillan offers 

 suggestions as to the classification of the Metaphyta, i.e. of the 

 higher forms of vegetable life. 



i SOCIETIES AND ACADEMIES. 



London. 

 Royal Society, April 28. — " On some Phenomena connected 

 with Cloudy Condensation." By John Aitken, F.R.S., 

 F.R.S.E. 



This paper is divided into two parts. In Part I. are described 

 I the different influences which cause the condensation of a 

 : jet of steam when mixing with ordinary air to become more 

 dense than it generally is, and in Part II. certain colour pheno- 

 i mena are described which have been observed when cloudy 

 j condensation is made to take place under certain conditions. 



I Part I. 



I Steam Jets. 



I It had been previously shown that when a jet of steam is 



electrified the condensation suddenly becomes very dense. In 

 I addition to electrification, it is found that this change in the 

 I appearance of the jet may be produced by other four causes. 

 I There are thus five influences capable of producing the dense form 

 ' of condensation. These are : ist, electricity ; 2nd, alar j^e number 



of dust particles in the air ; 3rd, cold or low temperature of the 

 j air ; 4th, high pressure of the steam ; and, 5th, obstructions in 

 1 front of the nozzle, and rough or irregular nozzles. 



1st. Electrification. 

 It is shown that the mere presence of an electrified body has 

 no influence on the steam jet. In order to produce the in- 

 creased density the water particles in the jet must be electrified, 

 either by direct discharge, or by an inductive discharge, effected 

 by means either of a point or a flame. 



The increased density produced by electrification is due to an 

 increase in the number of water particles in the jet, by the 

 electrification preventing the small drops coming into contact 

 by their mutual repulsions, in the same manner as the water 

 drops in Lord Rayleigh's experiments with water jets, which 

 scatter more when electrified than when not electrified. The 



j coalescence of the drops in water jets takes place only under the 

 disturbance produced by the presence of an electrified body, 



' while such a disturbance produces no effect on steam jets. 



I Oi her experiments point to the conclusion that the increase 

 in the density is due to an increase in the number, and not to 

 an increase in the size, of the drops. For instance, if steam is 

 blown into a receiver full of air in which there are many nuclei, 

 the condensation is dense, and, if there are few nuclei, the 

 clouding is thin. 1 he same holds good for the clouding pro- 

 duced by expanding moist air. If many dust particles be 

 present, the clouding is dense ; if few, it is thin. The action of 

 the electricity does not seem to be positive, as it has no effect 

 on a mixture of hot moist air and cold air. It seems rather to 



NO. II 78, VOL. 46] 



