142 



NA TURE 



[December 12, 1901 



Dalmatia, showing that the two species are extremely difficult 

 to separate, even if they are not identical. —Mr. C. P. Pickett 

 exhibited varieties of -J ;-^;'H»;/j /rt//;/a and A. aglaia from the 

 New Forest. — Mr. C. J. Watkins sent for exhibiiion micro- 

 photographs of the larva in its case and the perfect insect of 

 an Oxyethiia, one of the HydrofitilidaCy a family of Micro- 

 Truhoptera: these had been taken by Mr. Mearns, of Aberdeen. 

 Also a drawing made by himself under the microscope of a larva 

 (in its case) of the same genus. 



Royal Microscopical Society, November 20.^Mr. Wm. 

 Carruthers, F.K.S., president, in the chair. — Four microscopes 

 of great interest were presented to the Society. Descriptions of 

 three of these prepared by Mr Nelson were read. With regard 

 to one made by Powell and Lealand in 1848, Mr. Nelson 

 writes : — This form was the first instance in which the micro- 

 scope was hung in a tripod, and it was also the first where the 

 fine adjustment moved a nose-piece by means of a lever inside a 

 bar movement, and this specimen must have been about the 

 last microscope made with the fine-adjustment screw at the side 

 of the bar, for it was in this year, 1848, that the screw was 

 placed vertically above the lever, where it has remained ever 

 since. Other features were referred to, and Mr. Nelson 

 characterised it as historically an important and not very common 

 form of Powell and Lealand's microscope. The next micro- 

 scope described was an old one made by Hugh Powell, certainly 

 before 1841, as in that year Mr. Lealand joined the firm, and 

 his name would have been coupled with that of Powell, and the 

 presence of a substage condenser prevents it being dated earlier 

 than 1839. An important feature is the stage, which has an 

 arrangement for focussing by means of three wedges, moved by 

 a micrometer screw. The stage has also a transverse micro- 

 meter movement for the measurement of objects. The third 

 microscope was made by John Cuff. The date of its intro- 

 duction was 1744 and it was called "A New Constructed 

 Double Microscope." After the John Marshall microscope this 

 is historically one of the most important instruments in the 

 Society's collection. The other microscope presented was made 

 by Plossl and Cie, Vienna, and has already been described in 

 theyti;</'«n/ of the Society. — Messrs. R. and J. Beck exhibited 

 a new pattern microscope embodying several new features. 

 The substage was fitted with coarse and fine adjustments and 

 means of throwing out the condenser while it was in focus. 

 The stage, 5 inches diameter, was rotating and graduated on 

 the periphery, with a removable mechanical stage graduated as 

 a finder. The body was very short, fitted with double draw 

 tube, which allowed the body to be extended to 11 J inches. 

 The body was fitted with Ashe's new double fine adjustment. — 

 Mr. Conrad Heck gave an exhibition of antipoints, and said they 

 were extremely difficult to show on account of the troul)le there 

 was in obtaining points of light sufficiently small and bright, 

 and it was only possible to obtain faint images with so much 

 diffused light as there was in that room. There were six 

 microscopes, all having A-inch objectives, and the points of 

 light in the first two cases were produced by minute apertures 

 in tinfoil, in the others the light was reflected from smaU mercury 

 globules. With the first microscope a point of light was viewed 

 with 4-'nch objective of ordinary aperture and showed a /o/;;/ 

 of light surrounded with faint diffraction circles. With the 

 second microscope a similar point of light was viewed with a 

 A-inch objective of very small aperture and showed a disc of 

 light and diffraction rings. The other microscopes showed the 

 effects produced by placing various stops behind the objectives, 

 and also by viewing the point of light through a grating which 

 extended the whole aperture of the objective. Mr. J. W. 

 Gordon said he had listened with great interest to Mr. Beck's 

 explanation of the demonstration and was anxious to see the 

 examples, and no doubt the experiments would demonstrate the 

 existence and appearance of the antipoint in each case ; but there 

 was another and equally important image which he would like 

 to see and that was the antipoint which was formed in the eye, 

 and he hoped some day Mr. I3eck would be able to give a 

 demonstration of this. — A paper on .stereomicrography, by 

 Prof. G. P. Girdwood, of M'Gill College, Montreal, was read 

 by the secretary. Prof. Girdwood's method of obtaining 

 stereo-microphotographs was by placing the slide or object in a 

 tilting frame attached to the stage of the microscope. The 

 frame with the object was tilted to one side to the proper angle 

 and a photograph was taken ; the frame was then tilted to an 

 equal amount in the opposite direction and another photograph 

 was taken. Prints from the negatives were then mounted in 



NO. 1676, VOL. 65] 



the usual way to form stereoscopic pictures. The paper was 

 illustrated by a diagram on the blackboard, and a specimen of 

 the stereoscopic photographs, placed in a stereoscope, was passed 

 round the room. 



Duni.iN. 

 Royal Dublin Society, November 20. — Prof. W. Noel 

 Hartley, F.R.S., in the chair. — Prof. T. Johnson gave an 

 account of the results of field experiments he had conducted 

 during the past two years in the west and north-west of Ireland 

 in the prevention of "smut" (Usiilago av.nae, luni.) \n aMs. 

 The fungicides used were potassium sulphide (weak and strong 

 solution), copper .sulphate, formalin alone, and followed by 

 ammonia, and the new fungicide "sar" (essentially sodium 

 sulphide) recommended by the United States Department of 

 Agriculture. The latter was found by the author to be the 

 most efficient remedy. — Dr. F. T. Trouton, F. R.S., described 

 some experiments made by him at the request of the late Prof. 

 G. F. FitzGerald, in which it was sought to delect an effect 

 depending on the relative motion of the earth and ether. A 

 charged condenser placed with its plates edgeways to its motion 

 through the ether should possess a magnetic field. The question 

 to be investigated was the source of the energy for- this field. 

 FitzGerald's supposition was that at the moment of charging 

 the condenser should experience an impulse in the direction 

 opposed to its motion and on discharging in the direction of 

 motion. A condenser was therefore delicately suspended at 

 the end of a cross-arm with a balance weight at the other end 

 held by a torsion wire. The arm stood north and south and it was 

 sought to detect at 12 o'clock if there was an impulse acting 

 on the condenser when it was charged and discharged. This 

 was effected synchronously with the period of the apparatus 

 by a clock. No effect was observed though the calculated 

 effect was long within the range of delicacy. FitzGerald had 

 anticipated the possibility of a negative result being obtained 

 through the same cause as was suggested by him and Lorenz 

 to account for the negative results obtained by Michelson and 

 Morley in their interference experiments, namely, the alteration 

 in the weight of matter with direction of motion through the 

 ether. The alteration thereby produced in the electrostatic 

 energy would in this way provide [the necessary energy for the 

 magnetic field. The author pointed out that if it be thought 

 that the energy from the magnetic field is attributable to the 

 charging battery, it follows that charge condensers tend to set 

 themselves at right-angles to the earth's motion through space. 

 For on this hypothesis a condenser charged in the latter position 

 and rotated must have work done on it to energise the magnetic 

 field thereby produced. Thus, in this case it would be a couple 

 that should be looked for and not a directed impulse. He 

 proposed to test this by delicately suspending a light condenser 

 charged to a high voltage. It was also pointed out that if this 

 were true it would be possible to obtain continuous rotation 

 thereby, and thus to construct a machine to utilise the vast 

 stores of energy in the earth's motion through space. — Prof. 

 W. N. Hartley read a paper on haze, dry fog and hail. Last 

 February a paper by the author, conjointly with Mr. Hugh 

 Ramage, was communicated to the Royal Society, on the 

 mineral constituents of dust and soot from various sources. Solid 

 particles brought down by rain, hail, snow and sleet were sub- 

 mitted to analysis by means of the spectrograph, an instrument 

 by which the composition of very minute quantities of substances 

 is ascertained by photographing their spectra. For comparison 

 with these different kinds of dust, and to ascertain their origin, 

 the spectra of various other kinds of matter were photographed, 

 for instance, meteorites, volcanic dust, soot, and flue dust from 

 different chemical works and iron smelting furnaces. The result 

 of this examination showed that the origin of the dust could in 

 certain cases be ascertained from its composition. In the 

 present paper the author described the discharge of vast volumes 

 of dust and fume at very high temperatures into the upper at- 

 mosphere which he had observed in furnace operations at various 

 metallurgical works in England and Wales. He had arrived at 

 the conclusion that such material as had fallen in Ireland was 

 the product of the industrial centres of South Wales or South 

 Slaflordshire and possibly the pottery district of North Stafford- 

 shire. In certain cases it may have come from the centre of 

 the alkali manufactures about Widnes in Lancashire and Run- 

 corn in Cheshire. There is also a likelihood that the neigh- 

 bourhood of Glasgow contributes a good deal, as, for instance, 

 on the occasion in iSgS, when with a slight northeasterly wind 

 black rain fell in Ireland over an area of 500 square miles. 



