June i8, 1896] 



NA TURE 



159 



which the integral amount, during long periods of time, probably 

 reaches five, or even ten seconds. In particular it seems that 

 between 1769 and 1789 a retardation of the eaith's rotation took 

 place, and another between 1840 and 1861. Towards 1862 this 

 slackening was followed suddenly by a well-marked acceleration, 

 which possible persisted up to 1870." 



It may be added that the supposed variation does not seem to 

 account for the lunar inequalities to which reference has been 

 made. 



THE LADIES' CONVERSAZIONE OF THE 

 ROYAL SOCIETY. 



T^'HE second of the two annual conversaziones of the Rojial 

 Society — the one to which both ladies and gentlemen are 

 invited — was held in the rooms of the .Society at Burlington 

 House, on the evening of Wednesday in last week. As many 

 fif the scientific novelties exhibited were sh')wn at the conversa- 

 zione held in May, and have already been described in these 

 columns (May 14), it is unnecessary to refer to them again. 

 Only the new exhibits are therefore described in the present 

 report. 



In addition to Mr. Herbert Jackson's demonstration of the 

 various degrees of phosphorescence of different subjects under 

 the action of Riintgen rays, several other exhibits were 

 devoted to methods used and results obtained with the rays. 

 Prof. S. P. Thompson showed the prnduclion of electric dust- 

 shadows by Rdntgen rays. When the rays are allowed to fall 

 upon an electrified sheet of aluminium pl.iced above a plate of 

 ebonite, they carry electric charges to the plate and electrify it. 

 If objects of metal are laid on the ebonite sheet they intercept 

 the Rcintgen rays, and the part of the ebonite surface imme- 

 <liately shaded by them does not become electrified. On 

 removing the ebonite plate and dusting upon it Lichtenberg's 

 powders (mixed sulphur and red lead), the electric shadows 

 become visible. 



Prof. Thompson also showed a number of experiments on 

 Riintgen's rays, viz. : (a) Cryptoscopic use of luminescent 

 screens (revealing contents of packages, bones of hand, &c. ) by 

 employment of focus tube (Jackson's pattern) ; (b] discharge of 

 electroscope by Riintgen rays ; (i-) new forms of X-ray tubes, 

 including one for insertion in mouth ; (d) apparatus of Ebert for 

 producing luminescence by electric oscillations ; (s) stereoscopic 

 Riintgen-ray photograph of rabbit. 



Electric discharges in vacuum was the subject of exhibits by 

 Messrs. Siemens, Bros., and Co. The exhibits were (l) a 

 facsimile of Dr. Wm. Watson's vacuum tube of 1751. This was 

 the first apparatus ever constructed for experiments on the 

 electric discharge in a vacuum. The discharge from a Leyden 

 jar passed through ten inches, and that from africtional machine 

 through three feet, the whole length of the tube. (2) Facsimile 

 of Lord Cavendish's double barometer of 1751, used by Dr. 

 Wm. Watson in his researches. (3) P'acsimile of Dr. Wm. 

 Morgan's .shortened barometer of 1785. Dr. Morgan, by long- 

 continued boiling of the mercury in a b.uometer tube, produced 

 a vacuum of such excellence that no discharge would pass, and 

 equal, therefore, to that in a Hittorf or Crookes' tube of the 

 present day. It is probable that it would have sufficed for the 

 production of Rontgen rays. (4) Apparatus for showing electric 

 discharges at different degrees of exhaustion from 70 mm. to 

 o mm. (5) Photographs obtained by means of Rontgen rays, 

 showing relative transparency of different kinds of wood, 

 minerals, and glass. 



A series of striking Rontgen photographs was shown by Dr. 

 Macintyre. The marvellous advance made in Rontgen photo- 

 graphy will be understood from the following statement of the 

 subjects of Dr. Macintyre's pictures: (l) Hard Structures. — 

 Life-sized photographs of different parts of the human skeleton, 

 including the spine, ribs, shoulder, elbow and other joints of 

 the botly. Some of the negatives were 24 by 20 inches. (2) 

 Animal Kingdom. — A series of the animal kingdom, such as 

 the fish, frog, adder, &c. (3) Soft Tissues of the Body in 

 Health and Disease. — Human heart in the living adult subject. 

 The same in health and disease, also the tongue, tissues of the 

 neck, including the larynx, .Jtc. (4) Ins/.uitaiteous Photographs 

 of Different Ohjects. — The time of exp isure was unknown, but 

 the most rapid picture shown was taken with a single flash of 



NO. 1390, VOL. 54] 



the tube, due to one vibration of the interrupter of a ten-inch 

 spark coil. 



Mr. J. y. H. Teall exhibited a series of photographs of the 

 electric discharge at various stages during the exhaustion of a 

 Crookes' bulb of the Jackson type. 



A small dynamo for measuring the permeability and hysteresis 

 of iron was exhibited by Prof. W. E. Ayrton and Mr. T. 

 Mather. The specimen to be tested, which may be in the form 

 of a round bar or a bundle of thin plates, forms the yoke of the 

 dynamo, and through a coil surrounding it is passed the 

 magnetising current, the winding of this coil being .so arranged 

 that the current in amperes is numerically equal either to the 

 magneto-motive force per centimetre of the bar, or to one-tenth 

 of that value. When the armature is run at a speed of 11 50 

 revolutions per minute, the induction per square centimetre in 

 the bar is approximately equal to 10,000 times theE.M.F. in 

 volts produced. Hence not merely the magnetising current but 

 also the induction is measured by a steady deflection, and not, 

 as is usual, by the instantaneous swing of a ballistic galvano- 

 meter. The magneto-motive force required for the air-gap and 

 joints is determined experimentally by the use of a standard bar 

 whose B H curve is accurately known. 



Mr. T. Frith demonstrated the different effects produced by 

 superimposing a small alternating current on a direct current 

 arc according as cored carbons or solid carbons are employed. 

 When a small alternating current is superimposed on a direct 

 current arc formed with cored carbons, the oscillations of poten- 

 tial difference and current are in the satne direction for all 

 frequencies higher than about I \ periods per second. On the 

 contrary, if the carbon be solid, the oscillations of potential 

 difference and current are in the opposite direction for all 

 frequencies tried up to 256 periods per second. This difference 

 was exhibited by the visible motion of ammeter and voltmeter 

 needles. 



Microscopic internal flaws inducing fracture in steel axles, 

 rails, and propeller shafts were shown by Mr. T. Andrews. 

 This exhibit consisted of a series of accurate micrographs taken 

 at a high magnifying power, illustrative of the microscopically 

 visible and tangible micro-flaws, almost invariably present in 

 considerable number, in steel railway axles, rails, tires, propeller 

 shafts, &c. The presence of these germs of metallic disease in 

 steel (mostly due to sulphur and other impurities) greatly in- 

 fluences the deterioration by fatigue of the metal, and they are a 

 potent factor in inducing the sudden fracture of engineering 

 constructions in steel. 



Mr. 7. Macfarlane Gray exhibited a multiplication frame. In 

 this contrivance, for obtaining the product of two multidigital 

 numbers, product cards, as on " Napier's rods," are set for one 

 of them upon a sole frame, and sliders on a grid are .shifted to set 

 up the other. Each slider has a pane of plass at mid-length. 

 The grid is fitted to the sole frame upon a pair of stepped 

 guides, and is slid along over the cards one figure at a time. At 

 each step the component products in one of the vertical columns 

 of the common multiplication rule are exhibited at the panes and 

 added mentally. In this N>ay the final product is obtained 

 without transcribing the intermediate products. 



Exhibits illustrative of applications of the mathematical theory 

 of frequency were shown by the Applied Mathematics Depart- 

 ment of the University College, London. They included : (l) 

 Diagram illu.strating the relative variation of different organs in 

 men and women of diverse races, by Miss Alice Lee, G. U. Yule, 

 and K. Pearson. (2) Diagrams showing that 25 per cent, of 

 the married population produce 50 per cent, of the next genera- 

 tion — Reproductive Selection, by K. Pearson. (3) Diagrams 

 illustrating barometric frequency over the British Isles, by Miss 

 Alice Lee, C. Jakeman, and K. Pearson. (4) Frequency re- 

 cording barometer, by G. U. Vule and Cambridge Instrument Co. 

 (5) Amplified integrator for finding mean, mean square and mean 

 cubic deviations, and frequency skewness, by Amsler-Laffon. (6) 

 Prof. Ranke's craniophor, used in comparing variation of skulls, 

 as determined by English and German methods, by A. Martin- 

 Leake and K. Pearson. (7) Skew binomial machine, by G. U. 

 Vule. (8) Model of contour-tracer for finding areas of section 

 of small objects. 



Stereoscopic views of algebraic spherical catenaries and 

 gyrostat curves were exhibited by Prof. A. G. Greenhill and 

 Mr. T. I. Dewar. The mathematics of the spherical catenary 

 are discussed in a paper by Prof. Greenhill in the volume of 

 the Proceedings of the London Mathematical Society for the 

 current year, and a diagram of a closed algebraical one with five 



