142 



NATURE 



[December 6, 1894 



subject ; of these thirty-tno received the University's diploma 

 in Public Health. 



Mr. H. Vule Oldhim, Uuiversi'y Lecturer in Geography, 

 has been admitted by incorporation to the degree of M..\. 



The i'nivenity Reporter of Decembers contains a full report 

 of the speeches delivered at a meeting in King's College for the 

 purpose of promoting the foundation of a memorial library of 

 Oriental literature in honour of the late Prof. Robertson Smith, 

 editor of the Encydop^idia Brilnnnica. 



SCIENTIFIC SERIAL. 



Ariuri.ati Melioroh^i\a! yoiirna/, November. — Cyclonic pre- 

 cipitation in New England, by Prof. W. Upton. A list of 

 cyclones was made out, including nearly all in which the pre- 

 cipitation had been general over New England, and the amounts 

 and distribution noted on maps, with regard to the track of 

 the minimum pressure. The velocity with which the storms 

 passed r.^nged from fifteen to sixty miles per hour. The tables 

 show that the heaviest rainfall is rarely found along the central 

 path of the storm. Of the cyclones which came from the west 

 atross New England, only ten out of sixty-nine had their heaviest 

 precipitation on or nearthe storm-path, while forty-five had the 

 maximum area on the right of the storm-track ; similarly, out 

 of eighty-four cyclones which moved from the west mar New 

 England, seventy-three had their maximum precipitation south 

 of the storm-track. Further comments are reserved until the 

 results of a study of the storms coming from the south are given. 

 — The barometer at sea, by T. S. O'l.ear)'. This paper deals 

 with observations made chiefly by captains of American vessels. 

 The author considers that a great step forward was made when 

 the number of observations was reduced from twelve to one 

 daily, the result being that the number of observers has increased 

 nearly eight-fold. Another valuable feature is that the leaves 

 of the log-books are forwarded to the central office as soon as 

 opportunities are offered, so that the captains can see their 

 observations made use of without delay. A simple plan for 

 obtaining comparisons of the barometers has been adopted with 

 very satisfactory results. The observers when in port record 

 readings at certain hours, and forward them on post-cards to the 

 central office ; a copy of the "corrections" is immediately 

 returned to them, and copies filed for use and future reference. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, November 15. — "The Pigments of the 

 Pieridie. A Contribution to the Study of Excretory Substances 

 which function in Ornament." ByF. Gowland Hopkins. 



The wing-scalesof the white Pieridx are shown to contain uric 

 acid, this substance practically actingasa white pigment in these 

 insects. A yellow pigment, widely distributed in the group, is 

 shown to be a derivative of uric acid, and its artificial production 

 as a bycproduct of the hydrolysis of uric acid is demonstrated. 

 That this yellow pigment is an ordinary excretory product of 

 the animal is indicated by the fact that an identical subst.nnce is 

 voided from the rectum on emergence from the pupa. 



These excretory pigments, » hich have well-marked reactions, 

 are apparcnily confined to the Pieiidjc, and are not found in 

 other Rhopalocera. This fact enables the observation to be 

 made that when a pierid mimics an insect belonging to another 

 group, the pigments of the mimicked and mimicking insects, 

 respectively, arc cliemic.illy quite distinct. 



Other pigments existing, not in the scales, but between the 

 wing membranes, are described, and are ■'hown sometimes to 

 function in ornament. The analysis, and the properties of the 

 yellow scale pigment are fully discussed in the paper. 



Physical Society, November 23. — Prof. Riicker, F.R S., 

 President, in the chair. — Mr. Womack read a paper on a 

 modification nf the li.illistic galvanometer method of determin- 

 ing the electromagnetic capacity of a condenser. The con- 

 denser is placed in parallel with one arm (.S) of a Whcalstone's 

 bridge arrangement of non-inductive resistances. A balance 

 for st?.vly currents having been obtained, the condtnser is 

 placed in circuit, and the throw on depressing the battery key 

 determined. The condenser is then thrown out of circuit, and 



NO. I 3 ID, VOL. 51] 



the proportionality of the arms of the bridge disturbed by 

 changing the value of S to S -F i/S. The steady deflection 

 due to this change is then read. From these two reading*; and 

 the known values of S and ./S the capacity is immediately 

 determined. In practice readings of dttlection may be taken 

 with equal positive and negative values of ./S. To avoid 

 changes of E.M F. of the battery, the author finds it best to 

 use a reversing key in the battery circuit, and to observe the 

 throw on reversing the current instead of on simply breaking 

 it. One advantage of the method is that there is no need to 

 know the galvanometer- or battery-resistance, and the author 

 points out that it may be of service in the simultaneous deter- 

 mination of the resistance and of the joint capacity and 

 inductance of a submarine cable or of a telephone or telegraph 

 line. Prof. Perry asked what were the .idvantages of the 

 method as compared with the Rayleigh-Sumpner method. 

 Mr. Bl.ikesley thought that the correction for damping in the 

 ballistic part of the experiment might be avoided if in the 

 second part the disturbance of balance due to the incremen'. 

 </3 were measured by half the first throw of the needle oninakini; 

 the galvanometer circuit, instead of by the steady deflection. He 

 doubted whether reversing the current in the battery circuit 

 would have just twice the effect of simply breaking the circuit. 

 In reply, Mr. Womack said he had not tried the method of 

 reading suggested by Mr. Blakesley, but with regard to the re- 

 versing of the battery circuit, that w.as found to give in practice 

 as nearly as possible twice the deflection which resulted from 

 simply breaking. — .\ paper, by Prof. S. P. Thcmp^on and Mr. 

 Miles Walker, on mirrors of magnetism, was re.id by Prof 

 Thompson. It was pointed out that, corresponding to the theory 

 of electric images produced by insulated conductors, there is a 

 theory of magnetic im,iges produced by bodies of infinite mag- 

 netic permeability. A magnet pole in the latter theory is the 

 analogue of an electric charge in the former, and a body of in- 

 finite magnetic permeability is the analogue of an insulated con- 

 ductor (which is electrostatically indistinguishable from a body 

 of infinite dielectric capacity). Experiments were made to de- 

 termine how far the magnetic images due to thick sheets of iron 

 accorded with those deduced by theory for the case of infinite 

 permeability. The image of a north pole in an infinite plane 

 sheet should consist of a south pole of the same strength at a 

 point coinciding with the optical image of the north pole, to- 

 gether with an equal north pole distributed uniformly over the 

 surface of the infinite sheet, as a free electrical charge would be, 

 and so exerting no finite action. Working at distances of a 

 few inches in front of the surface, a sheet of iron a few feet in 

 length and breadth, and a couple of inches thick, was found to 

 realise the theoretical conditions with very tolerable exactness. 

 In a coil of wire placed on one side of the sheet a current was 

 started or stopped, and the electromotive impulse produced in a 

 subsidiary exploring coil was detected by means of a ballistic 

 galvanometer. That the eflect of the actual mirror 

 was equivalent to that of the theoretical image, was 

 verified by substituting for the iron a coil equal 

 and similar to the first, and coinciding wiih its optical 

 image. Sending the same primary current as before round 

 the two coils (with due regard to its direction in the second coil), 

 hardly any appreciable difference in the secondary impulse w.as 

 observed. This was found to hold good whether the original 

 primary coil had its axis peipcndicular or oblique to the plane 

 of the magnetic mirror. Some observations on spherical sheets 

 were also recorded, but in this case the conclusions were less 

 simple. The paper was followed by a discussion, in which Mr. 

 Boys, Prof. Petry, Prof. Ayrton, Dr. Burton, Mr. W. Bailey, 

 and Prof. Carey Foster took part. — Prof. Ayrton exhibited a 

 student's apparatus for verifying Ohm's law, designed by him- 

 self and Mr. Mather. The current flowing through a circuit is 

 to be measured (not necessarily in terms of any defined unit) by 

 means of a galvanomclc-r, while the potential. diflerence between 

 two fixed points is measured by means of an idioslatic electro, 

 meter. Within small limits of experimental error, the current 

 and potential-dilTerence ore found to vary in the same pro- 

 portion ; but the electrometer and its manner of use constituted 

 the chief interest of the paper. The fixed and moving parts 

 (inductors and needle^i are alike cylindrical inform (the term 

 being understood in its most unrestricted sense), and the 

 generating lines are vertical. There is a vertical axis of sym- 

 metry, .such that the disposition of these cylindrical parts would 

 remain unchanged if the instrument were rotated through 180* 

 about the axis. The needle is hung by a very thin phosphor- 



