478 



NA TURE 



[March 17, i. 



The Btillettino of the Italian Botanical Society is now pub- 

 lished apart from the Nnovo Giornale. The first number contains 

 reports of the papers read at the annual meeting, held at Naples 

 in August, and of the regular meetings held since till the end 

 of the year, and of the discussions which followed. Among 

 the more noteworthy papers may be mentioned the following : — 

 On a new carpellary theory, by Signor F. Pasquale, who main- 

 tains that the carpel is not derived, as has been generally sup- 

 posed, from the modification of a single leaf, but from the 

 concrescence of two, or sometimes of three leaves, which nnite 

 in the formation and nutrition of the ovules and seeds. — On the 

 floral structure and process of pollination in some species of 

 Nigella, by Dr. A. Terracciano. — On the period of formation 

 of the inflorescence within the bud of the vine, by Signor U. 

 Martelli. — On the non-sexual propagation of Cynomorium 

 coccineum, by the same writer, who has established its parasitism 

 on Alriplex nuvimularia. — Prof. G. Arcangeli also describes the 

 results of experiments on the cultivation of this plant, which he 

 finds to be parasitic on many hosts. — On earthquakes and vege- 

 tation, by Signor A. Goiran. He finds the eff'ects of seismic 

 motions in the earth to be the more rapid germination of seeds, 

 as well as a more rapid growth of the young plant. — Signor E. 

 Tanfani has a paper on the teaching of botany in gymnasia, 

 which he considers to be in a very backward state in Italy. 



The Botanical Gazette for January contains two interesting 

 original papers : — Herr A. F. Foerste speaks of the relationship 

 of autumn- to spring-blossoming plants, and concludes that late 

 autumn-flowering plants may be divided into two classes — those 

 which have developed from summer-flowering plants by the 

 increase in the number of internodes with their appendages 

 and the gradual retardation of growth, and those which have 

 developed from spring-blossoming plants by the premature 

 development of buds destined to flower during the ensuing 

 spring. — Mr. H. L. Russell discourses on the effect of me- 

 chanical movement on the growth of certain plants. The 

 experiments were made chiefly on certain yeast-fungi ; and the 

 general results were that the development of filaments was 

 hindered by shaking ; but that strong agitation greatly increases 

 the activity of cell-division, while it diminishes the intensity of 

 fermentation. This may be compared with the fact mentioned 

 above relative to the eff'ect of earthquakes on the growth of 

 plants. 



The greater part of the number of the Nuovo Giornale 

 Botanico Italiano for January is occupied by a paper by Signor 

 A. Jatta, on the Lichens of Italy, accompanied by a very ela- 

 borate bibliography. — Signor C. Massolongo has a note on a 

 floral monstrosity in /asmimcm grandiflorum ; and Dr. R. 

 ■Cobelli a paper on the movements of the flower and fruit of 

 Erodium gruinwn. These movements belong to three organs — 

 the calyx, the upper portion of the style, and the mericarp— and 

 do not appear to be in any way connected with the pollination 

 of the flower, since the species is apparently self-fertilized, and 

 no pollinating insects were observed at any time upon it, 



SOCIETIES AND ACADEMIES. 

 London. 

 Physical Society, February 26. — Prof. W. E. Ayrton, 

 F.R.S., Past President, in the chair.— Prof. S. P. Thompson, 

 F.R.S., read a paper on modes of representing electromotive 

 forces and currents in diagrams. The author said he had found 

 it advantageous in some cases to depart from the usual methods 

 of representation, and he now brought the subject before the 

 Society in order to have it discussed and improvements sug- 

 gested. To indicate the directions of currents in wires seen 

 end-on, Mr. Swinburne had used circles with and without 

 crosses, but no symbol had been suggested for wires not con- 

 veying currents. He (Prof. Thompson) thought the plain 

 circle should be used for inactive wires. A circle with a dot in 

 the middle could then be used to indicate that a current was 

 flowing towards the observer, and a circle with a cross in it to 

 represent a wire conveying a current away. These meanings 

 could be recalled by considering the direction indicated by an 

 arrow, the dot showing the tip of the arrow, and the cross the 

 feathers. Some method of distinguishing between E.M.F. and 

 current was required. For this he proposed to use thin-stemmed 

 arrows with feathers for E.M.F. 's, and thick-stemmed ones 

 without tails for currents. In the case of electrical transmission 

 of energy, this convention had the important advantage that 



NO. I 168, VOL. 45] 



where the two arrows had the same direction, energy was being 

 given to the system, and where the arrows were opposite, energy 

 was leaving it. Mr. Maycock, he said, had recently published 

 a simple rule for finding the direction of magnetic force due to a 

 current of known direction in a wire. Grasp the wire with the 

 right hand, the thumb pointing in the direction of the current ; 

 the fingers will then encircle the wire in the direction of the 

 magnetic force. Dr. Fleming's well-known rule for induced 

 currents was also a right-hand rule, but as it referred to the 

 direction of currents, another rule was necessary when con- 

 sidering motors. By making the rule refer to E. M.F.'s, only 

 one rule was required for generators and motors. For alter- 

 nating currents the author found it convenient to draw polar 

 curves analogous to Zeuner's valve diagrams. Suppose a line 

 OP (Fig. i), representing the maximum value of an E.M.F. or 



current whose magnitude is a sine function of the time, 

 to revolve at uniform velocity about o; the intercepts 

 OQ, oq', &c., cut off by circles OQB, oq'd, will represent the 

 magnitudes at the times corresponding to the positions op and 

 op'. The effect of lag can also be represented in such diagrams. 

 In cases where the variables are not sine functions, the curves 

 OQB and oq'd are no longer circles. Polar diagrams represent- 

 ing the E.M.F. and current curves obtained by Prof. Ryan in his 

 transformer experiments were exhibited, and a working diagram, 

 illustrating the changes in three-phase currents, was shown. To 

 show the directions of induced E. M.F.'s in diagrams of dyna- 

 mos and motors, diagonal shading of the pole-faces was some- 

 times convenient ; the lines over north poles being drawn from 

 left to right downwards in the direction of the middle stroke of 

 the letter N, and those over south poles from left to right up- 

 wards. A conductor passing over a north pole from left to 

 right would have an E.M.F. induced in a downward direction, 

 as indicated by the slope of the diagonal lines. This method of 

 representation was used to show the ways of connecting up 

 multipolar drum armatures, the winding being supposed cut 

 along a generating line, unwrapped from the core, and laid out 

 flat in the manner adopted by Fritsche. In connection with 

 armatures, the author said a formula had been published by 

 means of which the nature of a winding consisting of a given 

 number of convolutions, and to be used with a given number of 

 poles, could be predetermined. This, he thought, would be 

 very useful in practice. Mr. Blakesley said the old method of 

 representing alternate current magnitudes by means of the pro- 

 jections of revolving lines, seemed preferable, for it left no 

 ambiguity as to the directions of the quantities. The method of 

 shading the poles also required that the direction in which the 

 diagram was to be viewed should be known before the direction 

 of the E.M.F. could be determined. Mr. Swinburne suggested 

 that the author might use a bow to represent E.M.F'., and 

 an arrow for current. He was glad to see that Prof. Thomp- 

 son recognized the differences in dynamos and motors, 

 and approved of the view that mnemonic rules should refer 

 to E.M.F. and not to current. The diagrams of drum 

 bindings would be very useful, and he hoped the author 

 would make the subject clear to ordinary workmen in 

 the next edition of " Dynamo-Electric Machinery." Prof. 

 Perry considered it undesirable to use polar curves for any- 

 thing but circles. In his opinion it was not sufficiently 

 known that any curve can be split up into a series of sine curves, 

 and each component dealt with separately ; the separate results 

 being added together in the end. Mr. Swinburne pointed out 

 that before one could analyze a curve in this way, the curve 

 must be known, and would probably have to be determined ex- 



