December 19, 1895J 



NATURE 



167 



SOCIETIES AND ACADEMIES. 



London. 

 Royal Society, November 21. — "On the Calibration of the 

 Capillary Electrometer." By George J. Burch, M.A. 



In two previous papers the author has described a method of 

 using the capillary electrometer for measuring rapid variations 

 of E.M.F. A sensitised plate, fixed to a balanced pendulum, 

 is carried with uniform velocity past a vertical slit, so that the 

 movements of the meniscus are recorded in a polar curve, in 

 which time is measured by the angular displacement, and the 

 position of the mercury by the radius vector. In such a curve, 

 the total indicated E.M.F. at any instant is the algebraic sum of 

 the P.D. corresponding to the distance through which the 

 meniscus has moved, and the I'.D. corresponding to the 

 velocity with which it is moving. In a good instrument 

 the latter is proportional to the subnormal to the curve 

 at that point. The validity of this method depends on 

 the use of an apparatus of which the time-relations correspond 

 to the formula r = ae -'^, and in the present communication the 

 author describes a practical method of determining the time- 

 constants of a capillary. The first step is the calibration of the 

 scale-readings. This is effected by fixing a glass millimetre scale 

 to the focussing screen, and measuring the E.M.F.s necessary 

 to produce a permanent excursion from the upper limit of the 

 slit to a series of points 5, 10, 15, &c., millimetres lower. For 

 the calibration of the subnormals two normal excursions are 

 photographed with the capillary in the same position. In one 

 the zero is below the field of view, and the movement is 

 directed upwards, and in the other the zero is raised above the 

 field of view, and the potentiometer wires reversed so as to 

 produce a downward excursion. 



The object is to obtain two curves in opposite directions 

 running right across the plates, the exact extent and relative 

 position of the excursions being immaterial. The subnormals to 

 these curves are measured at points 5, 10, 15, &c., millimetres 

 from the upper limit of the slit. The author shows that the 

 algebraic difference between the polar subnormals to correspond- 

 ing points upon two oppositely directed excursions is constant if 

 the time-relations of the instrument agree with the formula 

 r — a£-'^'. With some capillaries the velocity of the meniscus 

 may be different, for the same acting P.D., at different parts of 

 the tube. In such cases the multiplier which turns subnormal 

 readings into volts is proportional to the algebraic difference of 

 the subnormals for any given position of the meniscus. To find 

 the absolute value of this multiplier, a third photograph is taken 

 in which a normal excursion of known value starts from a zero- 

 point within the field of view. The subnormal to this curve is 

 determined for some one of the selected positions, and the 

 corresponding acting P.D. found by subtracting the electrical 

 .alue of its distance from the zero-line from the P.D. indicated 

 y the potentiometer. The shape of this curve at its origin 

 -hows whether the instrument is dead-beat. If the velocity of 

 the meniscus increases after the excursion has begun, the 

 capillary should be rejected. The entire calibration can be 

 completed in about two and a half hours, and the method is 

 applicable to any dead-beat instrument. The author concludes 

 with a criticism of recent papers by Prof. Einthoven on the same 

 subject. 



Physical Society, December 13.— Special General Meeting. 

 — Prof. Keinold, Vice-President, in the chair. — The resolution, 

 with reference to the change in the amount of the life-composition 

 fee, passed at the special general meeting held on November 22 

 last, was confirmed. The ordinary meeting was then held. — Dr. 

 [ohn Shield read a paper on a mechanical device for performing 

 the temperature corrections of barometers. The form of 

 barometer to which the author has adapted his device is that 

 devised by Dr. Colley ; it is intended for general laboratory use, 

 and is capable of being read to within 0"i mm. The barometer 

 tube can be moved in a vertical direction so that the lower 

 meniscus can be adjusted to the zero of the .scale. Attached to 

 the barometer tube is a thermometer with a horizontal stem, 

 passing in front of a scale which is fixed to the vertical scale of 

 the barometer. The graduations of this thermometer scale, 

 with thd exception of the one passing through the o°C. mark on 

 the thermometer, are inclined to the vertical, and are so spaced 

 that the reading opposite the end of the mercury column of the 

 thermometer gives directly the correction to be applied to the 

 observed height of the barometer (H^) in order to obtain the 

 reduced height (B<,). That is, the reading on the thermometer 



NO. 1364, VOL. 53I 



scale gives the value of Bt{0-y)i where $ and 7 are the co- 

 efficients of expansion of mercury and of the material of which 

 the barometer scale is composed respectively, and / is the tem- 

 perature. Mr. Boys admired the simple method the author had 

 adopted for plotting the corrections ; and said he always felt 

 that the trouble involved in applying small corrections ought if 

 possible to be avoided, or the correction would often be omitted. 

 Mr. Appleyard advised the placing of the bulb of the thermo- 

 meter within the barometer lube. Dr. Shield in his reply said 

 as the barometer was only intended to read to O'l mm., the 

 placing of the thermometer within the tube did not appear 

 necessary. — A paper by Prof. Rucker,on the existence of vertical 

 earth-air electric currents in the United Kingdom was, in the 

 absence of the author, read by Mr. Kay. In a paper read 

 before the British Association at Oxford, Dr. Schmidt stated 

 that he had expanded the components of the earth's magnetic 

 force in series, and had deduced expressions, two of which give 

 the magnetic potential on the surface of the earth in so far as it 

 depends on (i) internal and (2) external forces. The third 

 seiies represents that part of the magnetic forces which cannot 

 be expressed in terms of a potential, but must be due to 

 electric currents traversing the earth's surface. Dr. Schmidt 

 concluded that such currents amount on the average to about 

 o'l ampere per square kilometre. The author has tested 

 this conclusion, drawn from the state of the earth as a whole, 

 by means of an examination of the line integral of the mag- 

 netic force round a re-entrant circuit, taken in the United 

 Kingdom. The necessary data have been obtained from the 

 results of the magnetic surveys for the epochs 1886 and 1891, 

 carried out by the author and Dr. Thorpe. Two circuits called 

 the a and )8 circuits were selected, having their greatest extension 

 north and south, and east and west respectively. The work 

 done by a unit magnetic pole on traversing these circuits was 

 calculated for the epoch 1886 by means of the terrestrial lines 

 found for that date, and also for the epoch 1891 by means (i) 

 of the same lines when due allowance was made for secular 

 change, and (2) of the independent set of lines found by aid of 

 the 1891 survey. The same calculation was made for a third 

 circuit (7), using instead of the calculated terrestrial lines the 

 true values of the forces and declinations as deduced from the 

 nearest stations. The following table gives the results in 

 amperes per square kilometre. 



a By 



1886 ... -0-026 ... -0004 ... — 



1891(1)... -J-o-ooi ... -0005 ... — 



1891(2)... — ... — ... -o-coS 



From these figures the author concludes that there is not in the 

 United Kingdom, at any rate, a vertical current amounting on 

 the average to o*i ampere per square kilometre. — Mr. Watson 

 said a few words on the difficulty experienced in determining 

 the line integral in South Wales due to the presence of closed 

 curves. — The Society then adjourned till January 24, 1896. 



Zoological Society, December 3. — Sir W. H. Flower, 

 K.C.B., F.R.S., President, in the chair. — The Secretary read 

 a report on the additions that had been made to the Society's 

 menagerie during the months of October and November 

 1895, and called attention to the acquisition of a specimen ot 

 the wild goat of the island of Giura, in the /^igean Sea ( Capra 

 dorcas). — Mr. Tegetmeier exhibited a specimen of a crab with 

 a supernumerary claw. — A communication was read from Dr. 

 G. Stewardson Brady, F.R.S., containing a supplementary 

 report on the Crustaceans of the group Myodocopa obtained 

 during the Challenger expedition, to which were added notes 

 on other new or imperfectly known species of this group. — Mr, 

 F. E. Beddard, F.R.S., read papers on some points in the 

 anatomy of Pipa aiiiericana and on the diaphragm and the 

 muscular anatomy of Xettopus. The author added remarks on 

 the affinities of these two anomalous Batrachians, which he 

 considered to have been correctly placed together in the .system. 

 — Mr. W. Bateson, F.R.S., gave an acount of the colour- 

 variations of a variable beetle of the family Chrysomelida; 

 {Goniocfena variabilis) statistically examined. It was shown 

 that the individuals are chiefly either red spotted with 

 black, or else greenish grey striped with ■ black. All inter- 

 mediates occurred, but were less common than the type- varieties. 

 These facts illustrated the phenomenon of organic stability. — A 

 communication from Mr. R. Lydekker, F.R.S., contained re- 

 marks on the affinities of the so-called extinct Giant Dormouse of 

 Malta. The author stated that this extinct rodent did not belong 



