December 24, 1891] 



NATURE 



191 



The chief discovery of interest was that in hanging drops 

 the author traced the evolution of this "rose-yeast" into 

 a large complex mycelium, bearing conidia, and so like some 

 of the Basidiomycetes that it may almost certainly be re- 

 garded as a degraded or "torula" stage of one of these 

 higher fungi. Full descriptions and figures are given by the 

 author. 



The form Mycoderma cerevisia: was thoroughly examined. 

 The author's results confirm what is known as to its aerobian 

 characters. Statements as to its identity with Oidiiim lactis 

 were not only not confirmed, but the author grew these two 

 forms side by side, and maintains their distinctness. Nor could 

 he obtain spores in this fungus, thus failing to confirm earlier 

 statements to the contrary. fie regards it as probable that oil- 

 drops have been mistaken for spores ; he also finds that in later 

 stages of fermentation by this organism a strong oily-smelling 

 body is produced. 



With regard to Bacterium aceti, the author has nothing new 

 to add. A point of some interest was the repeated production 

 of acetic ether, which scented the laboratory, when this Schizo- 

 mycete was growing in company with the small white aerobian 

 top-yeast referred to under (3). Full details regarding the rest 

 of the organisms, which have nothing to do with the "ginger- 

 beer plant " proper, are given in the original paper. 



Physical Society, December 4.— Prof. W. E. Ayrton, 

 F. R.S., President, in the chair. — A paper on a permanent 

 magnetic field was read by Mr. W. Hibbert. The author had 

 noticed the approximate constancy of an "aged" bar magnet, 

 and he obtained still greater constancy by attaching pole pieces 

 to a bar magnet, of such a shape as to give a nearly closed circuit 

 of small " magnetic resistance." The pattern now described 

 consists of a steel rod i inch diameter and about z\ inches 

 long, with a cast-iron disk 4 inches diameter and | thick fixed at 

 one end ; the other end is fitted in a hemispherical iron shell 

 which surrounds the bar and comes flush with the upper surface 

 of the disk. An annular air space less than xV inch wide is left 

 between the cylindrical surface of the disk and the inside of the 

 shell, and when the bar is magnetized, a strong magnetic field 

 exists in this space. To use this field for producing electro- 

 magnetic impulses, a coil of wire is wound in a shallow groove 

 on a brass tube which can slide axially through the annular 

 space, thus cutting all the lines. The tube is allowed to fall by 

 its own weight, a neat trigger arrangement being provided for 

 effecting its release. The instrument exhibited had 90 turns of 

 wire in the coil, and the total magnetic flux across the air space 

 was about 30,000 C.G.S. lines. A large electro-magnetic im- 

 pulse is, therefore, obtainable even through resistances as great 

 as 10,000 ohms. Tests of three instruments show that there has 

 been practically no magnetic decay in seven months. The 

 author therefore considers them satisfactory, and is prepared 

 to supply them as magnetic standards. To facilitate calculation, 

 the number of lines will be adjusted to a convenient number, 

 say 20,000 or 25,000. Several uses to which the instruments 

 are well suited are mentioned in the paper, and a simple way 

 of determining permeability by the magnetometer method is 

 described. Mr. Blakesley thought the name given to the in- 

 strument was inappropriate, for it really gave a constant 

 impulsive E. M.F. Dr. Sumpner said the constancy of the 

 sensibility of d'Arsonval galvanometers was a measure of the 

 constancy of magnets having nearly closed circuits. Such in- 

 struments, in use at the Central Institution, had remained 

 unchanged for several years. Prof. S. P. Thompson admired 

 Mr. Hibbert's instrument, and thought it would be very useful 

 in laboratories. Standard cells, he said, were not always 

 reliable, and condensers were the most unsatisfactory' of electrical 

 standards. On the subject of permanency of magnets, he said 

 that Strouhal and Barus found that magnets with nearly closed 

 circuits were most constant, and that, to give the best results, 

 the hardness of the steel should be less the more closed the 

 circuit, Mr. Hookham had also found that by using a nearly 

 closed circuit, and reducing the strong magnetization by about 

 10 per cent., ijreat constancy could be obtained. Some years 

 ago he (Dr. Thompson) had tried the effect of ill-treatment on 

 magnets, and observed that touching or hitting a magnet with 

 non-magnetic material had little effect, whilst similar treatment 

 with iron or magnets affected them considerably. Suddenly 

 removmg the keeper of a magnet tended to increase the magnet- 

 ism, whdst putting a keeper on suddenly had the reverse effect. 

 Strouhal and Barus had also investigated the temperature co- 

 efficient of magnets, and found that this might be reduced by 

 NO. I 156, VOL. 45] 



subjecting the magnet to rapid changes of temperature after the 

 first magnetization, and then remagnetizing. Mr. W. Watson 

 inquired what was the percentage fall in strength of Mr. 

 Hibbert's magnets. The bars used in magnetic surveys had been 

 tested frequently, and they lost about 0-5 per cent, in 6 months. 

 The President asked what were the temperature coefficients of the 

 magnets described in the paper ? Mr. Evershed, he said, thought 

 it was between 001 percent, and 0-05 percent, for ordinary mag- 

 nets. He thought the instrument shown by Mr. Hibben would 

 be of immense value if the magnet was really permanent. By it 

 ballistic galvanometers could be readily calibrated, and, when 

 combined with a resistance box, it could also be used as a 

 standard for current ; for, since the constant of a ballistic galva- 

 nometer for quantity can be determined from its constant for 

 current, if the periodic time be known, conversely that for 

 current can be found from the constant for quantity. In some 

 instances this would be of great use. Speaking of the tempera- 

 ture coefficient of condensers, he said that in some cases the 

 specific inductive capacity of dielectrics diminished with rise of 

 temperature whilst in others it increased. Mr. Hibbert, in 

 reply, said he found the temperature coefficient of his magnets 

 to be, roughly, about 0-03 per cent,, but he had not investigated 

 the matter very carefully. In making his measurements no cor- 

 rection had been made for the variation of capacity of his con- 

 denser with temperature,— Mr. Walter Baily took the chair, and 

 the President communicated a note on rotatory currents. The 

 subject, he said, was probably familiar to most persons present, 

 for it had been frequently referred to in the scientific papers. 

 Alternate currents could be obtained from an ordinary direct 

 current dynamo by making contact with two points in the arma- 

 ture, say by connecting these points to insulated rings on the 

 shaft, and using extra brushes, A direct current motor similarly 

 treated transforms direct currents into alternating currents, 

 or into mechanical power. If two pairs of points in the 

 armature be selected, situated at opposite ends of two perpen- 

 dicular diameters, then two alternating currents differing in 

 phase by 90° can be obtained ; and by choosing suitable points 

 in the armature, two, three, or more currents differing in phase 

 by any desired angles can be produced. In ordinary motors the 

 connections for doing this would be troublesome, but the Ayrton 

 and Perry form, which has a stationary armature, lends itself 

 readily to this purpose, for contact can be made with any part of 

 the armature with great facility, A motor of this kind was 

 exhibited, in which contact was made with four equidistant 

 points on the armature. On connecting opposite points through 

 fine platinum wires, and running the motor slowly, the wires 

 glowed alternately, one being bright whilst the other was dark, 

 and vice versd, thus demonstrating the existence of two currents 

 in quadrature. When the four points on the armature were 

 joined to the four corners of a square of platinum wire, the 

 wires became incandescent in succession, the glow appearing to 

 travel round the square, and suggesting the idea of rotatory 

 currents. A Tesla alternating current motor was also driven by 

 two currents differing in phase by 90°, obtained from the arma- 

 ture of the Ayrton and Perry direct current motor above 

 mentioned. The ease with which currents differing in phase by 

 any amount can be obtained from such a motor led the author 

 to investigate theoretically the case of two circuits connecting 

 opposite ends of two diameters inclined at any angle, a. Call- 

 ing the currents in these circuits at any instant, A, and A», he 

 had found that 



Ai = 2«Eo 



multiplied by sin {pe+<l>) ; 

 where « = number of turns on armature per radian, 

 p — resistance of armature per radian, 

 - - resistance of external circuit in which current Aj 



passes, 

 ^2 = resistance of external circuit in which current Aj. 



Efl = maximum E.M.F. per convolution 

 / = angular velocity of rotation, and 



p( - -a )sino 

 tan<^- ^^ ^ 



''*+pl-p{l-»y OS a 



