400 



NA TURE 



\AugUSt 2 2, 1889 



former experiment, it be passed through a screen with a 

 hole in it (either square or a long slit at right angles to 

 the electric displacement), the position of interference, as 

 might be anticipated, was not shifted out as much as 

 before. In the rough experiment made, it was found to 

 occur at about 19 centimetres from the screen. 



It was now thought well to repeat the determination of 

 the index of refraction with a larger wall and metallic 

 reflector than had been used before, as this change of 

 phase might have affected the former results. But it was 

 found that it had not done so to a sensible extent. How- 

 ever, the result of these new experiments was finally to 

 give for paraffin, [x. = 175, and at the same time it was 

 found that the wave-length given by the "vibrator" was 

 68 and not 66 centimetres, as had been assumed. 



Two new knobs for the " vibrator " had been made, and 

 the fact had been overlooked that they were slightly larger 

 than the old ones, which gave a wave-length of 66 centi- 

 metres. These new knobs were electro-plated with gold, and 

 were a great saving of trouble, as they could be cleaned by 

 merely rubbing with paper ; apparently, the gold which 

 was carried across by the sparking in the form of a black 

 powder coming off, but some may have reburnished on. 

 It was a curious thing that, if the knobs were left un- 

 cleaned over-night, the next morning it was very hard 

 to get the black off, some molecular change probably 

 occurring. 



If the value of /i thus found be not in some way due to 

 the paraffin being in separate blocks, it would show a re- 

 markable anomalous dispersion for paraffin near these 

 curiously slow vibrations, and, as suggested by Prof 

 Fitzgerald, may be connected with the vibration periods 

 of atoms in the molecule, as it can hardly be connected 

 with the vibrations in the atoms themselves. It might 

 be interesting to investigate whether these slow vibrations 

 could cause dissociation, and thus lead to a photographic 

 method of observing them. It may also be allied with 

 ordinary electrolysis by very long period currents, as is 

 also suggested by Prof Fitzgerald. 



Assuming /ii = i 75,^ and A=68 centimetres, the thicknesses 

 of the walls in the " Newton's ring" experiment, as above 

 described, were wrong. However, it was found more con- 

 venient to alter the angle of incidence to suit the walls 

 than to change the thickness of the walls. Thus, the 

 mirrors were put at 25", which is the proper angle with 

 the above data for 10 centimetre and 20 centimetre 

 walls. On now repeating the experiment, better results 

 were obtained than I should have anticipated. When 

 the wall was 10 centimetres thick, continuous sparking 

 was easily obtained, but, when 20 centimetres thick, it 

 was only after much adjustment and patience that per- 

 haps one slight spark could be obtained. This was quite 

 sufficient, considering the nature of the wall, for it was 

 only built up of plates, which afforded internal reflections, 

 weakening the transmitted rays, and also since it requires 

 the sum of the effects arising from the multiple reflections 

 back and forward inside the wall to completely interfere 

 with the front, and some of these are lost at the edge of 

 the beam. Fred. T. Trouton. 



ICE GROWTH? 



CEVERAL of the Arctic Expeditions have instituted 

 •--^ observations on the rate of growth of the ice during 

 the winter, and in the " Contributions to Arctic Meteoro- 

 logy," vol. i., 1885, records of this nature are given for the 

 following stations : Gulf of Boothia, Assistance Bay, 

 Port Bowen, Walker Bay, Cambridge Bay, Camden Bay, 

 Princess Royal Islands, and Mercy Bay. The second 



' This value agrees with polarization experiments. No reflection was 

 obtained at its corresponding angle, while at tan-1 1-51 some sparks were 

 occasionally seen. 



^ Abstract of Dr. Stefan's paper, " Ueber die Theorie der Eisbildung, 

 insbesondere iiber die Eisbildung im Pola-Meere,';from ihe.\jSitz7tngsberichte 

 of the Vienna Academy. 



German Arctic Expedition has also undertaken such' 

 investigations and published results in its report (Leipzig, 

 1874). 



In the present paper these observations are compared 

 with the results of the theory of ice-formation, the basis 

 of which has been explained by the author in a paper 

 on some points in the theory of the conduction of heat. 



The theory gives for the thickness (X) of ice formed in 

 the time {t) the following formula, which is approximately 

 correct — 



V 3X/ Xo- 



In this formula {c) is the specific and (X) the latent heat 

 of ice ; {k) is the coefficient of conduction, {a) is specific 

 gravity, (/) is the temperature at the surface of the ice at 

 the time (/), {k) the sum of cold for the same time ; the 

 last is the sum of the temperatures counted downwards 

 from 0° C, from the commencement of ice formation up 

 to the time (/). 



The squares of the measured ice-thicknesses were taken 

 and multiplied by the factor contained in the above for- 

 mula, and the differences between the successive values 

 were divided by the sums of cold for the corresponding 

 intervals of time. The quotients for the different obser- 

 vations of each station differ in some degree from each 

 other. Those which are most regular are the Gulf of 

 Boothia, Assistance Bay, Port Bowen, and the German 

 Expedition. The mean values for these four stations are,, 

 respectively, 0877, 0-851, 0-869, and 0-878. Of the sta- 

 tions which show considerable differences. Walker Bay 

 gives 0-919, Cambridge Bay 0780, Camden Bay 0-791. 

 The smallest quotients are, 0-755 for Princess Royal 

 Islands, and 0-700 for Mercy Bay in the first winter, 

 whilst it is 0-810 for the second winter. 



We may take 0-87 as the normal value of the quotient. 

 If any station gives considerably less than this, it may 

 be concluded that some disturbance of the process of 

 ice formation has occurred, such as, eg., if the station 

 was affected by a warm current which brought up warmer 

 water, and so delayed the formation of the ice. 



The units for the figure 0-87 are the Fahrenheit degree, 

 the English inch, and the day. For Celsius, centimetres, 

 and the day, the figure would be 10-092. From it the 

 coefficient of conduction of Polar ice,/&, is 362-4. If the 

 second be taken as the unit of time, the value of k would 

 be 0-0042. 



DR. C. FORSYTH MAJOR'S DISCOVERIES IN 

 THE ISLE OF SAM OS. 



■\1/'E are glad to learn that Dr. H. Woodward, who has 

 ** just returned from Florence, has secured for the 

 Palaeontological Department of the British Museum 

 (Natural History) the valuable collection of Vertebrate 

 remains of Lower Pliocene age obtained by Dr. C. 

 Forsyth Major during the year 1887 in the island of 

 Samos, in the Turkish Archipelago. Dr. Forsyth Major 

 lately contributed to the Coinptes rendus (vol. cvii. 

 pp. 1 178-81) a preliminary notice of this collection. 

 Among the remains are a large number of forms speci- 

 fically identical with the mammals from the equivalent 

 deposits of Pikermi in Attica, Baltavar in Hungary, and 

 Maragha in Persia ; but there are also some new types, 

 which are of interest either from a distributional or 

 a purely zoological point of view. Among these new 

 forms is a species of ant-bear {Oryderopus), which 

 is the only representative of that genus yet known 

 beyond the Ethiopian region. A large pangolin, which 

 is estimated to have been nearly three times the size of 

 the West African Ma7iis gigantea, is made the type of 

 the new genus Pal(E07nams ; and is of interest as show- 

 ing how the African pangolins may have been connected 

 with those of India. Perhaps the most striking new 



