i8o 



NA TURE 



[June 22, 189; 



maxima ranging from 80° to 88° in many parts of the king- 

 dom, while on Monday the 19th instant, the temperature 

 reached 91° at Greenwich. This is the highest reading which 

 has occurred there in June since the year 1858, and it has not 

 been exceeded in any part of the summer during the last five 

 years. In the early part of the present week shallow depres- 

 sions passed over these islands causing the recurrence of 

 thunderstorms in many parts. These were accompanied by 

 smart showers in a few places, and by a considerable fall in the 

 temperature, the maximum in London on Tuesday being 24° 

 lower than on the previous day. The Weekly Weather Report 

 of the 17th inst. showed that the mean excess of temperature 

 ranged from 3° or 4° in England, to 6° in Scotland, and to 7° in 

 the north of Ireland. There was no rainfall whatever over the 

 greater part of England and Scotland. 



THEVatican Observatory has issued thethird volume of its Ptib- 

 blicazioni, containing xxiii -f 442 quarto pages and thirty plates. 

 The plan followed by Padre Denza is the same as in the pre- 

 vious volumes, and the work is produced in the same excellent 

 style. After quoting some historical documents relating to the 

 observatory, an account is given of the last general meeting of 

 the superintending Council and of the principal astronomical 

 and astrographic researches carried on at the observatory. 

 Although the magnetical and geodynamical sections are not yet 

 in order, several papers of special interest in these important 

 subjects are published. The meteorological section contains 

 hourly observations and results for the year 1891 ; in this 

 branch we specially notice a paper on the classification of clouds 

 by Sr. F. Mannucci, photographic assistant at the observatory, 

 illustrated by fourteen photographs taken at the observatory and 

 neatly printed by Dujardin of Paris. The classification adopted 

 is that proposed by Messrs. Abercromby and Hildebrandsson, 

 and consists of ten diiTerent kinds of clouds, divided into five 

 principal groups, according to the heights at which the various 

 forms are usually found. The last part of the work contains an 

 account of the proceedings of the ordinary meetings held in the 

 year 1892. 



Proisably few people are aware that there still exists in this 

 country a manufactory of gun and tinder-box flints, yet such is 

 the case. Mr. Edward Lovett, in the Illustrated Archceologist 

 for June, gives an interesting description of the flint industry 

 which has been carried on at Brandon, situated on the borders 

 of Suffolk and Norfolk, since the Stone Age. The methods 

 employed in the mining and fashioning of flints at that remote 

 period prevail, with little alteration, unto this day. In order to 

 break flint into pieces of convenient size, the worker places the 

 mass on his knee, and, by a dexterous blow with a hammer, 

 shivers it into fragments as easily as if it were chocolate. The 

 pieces are then split into flakes, and these, in turn, are fractured 

 into little squares which, with very slight trimming, become the 

 finished gun-flints. Most of the gun-flints are exported to 

 Zanzibar and other ports in communication with the interior of 

 Africa, but, besides these, large quantities of flints for tinder- 

 boxes are still made at Brandon. Tinder-box flints chiefly go 

 to Spain and Italy for use in isolated districts. It is a curious 

 fact, however, that the flint-and-steel method employed by pre- 

 historic man in making fire is better than matches in uncivilised 

 regions, and very moist climates. 



At a recent meeting of the Sociele Fran9aise de Physique a 

 note from Dr. Stephane Leduc was read, in which the corre- 

 spondant points out that the physiological effects of alternating 

 currents obtained from electrostatic machines are very different 

 to those up to now observed with ordinary alternating 

 currents of high tension and frequency. Thus, if the ter- 

 minals are held in the hands nothing is felt, although a con- 

 tinuous stream of sparks is passing between the dischargers. If, 

 however, the current is localised at one point on the skin by 



NO 1234, VOL. 48] 



1 



means of a rounded point, directly this point passes over 

 nerve, either sensory or motor, the nerve is excited throughout 

 all its length beyond the electrode. The sensation felt in the 

 sensory nerves allows of their distribution being accurately fol- 

 lowed, while the least displacement of the electrode on the 

 surface of the skin causes a cessation of all these effects. These 

 currents can in this way be used to localise the seat of nervous 

 excitation with much greater accuracy than has been hitherto 

 possible. 



The results obtained by Blondlot in his extensive research on 

 the capacity of polarisation have been confirmed by some recent 

 experiments of M. Bouty (see Proceedings of the Sociele 

 Fran9aise de Physique). M. Bouty has chiefly studied the case of 

 melted electrolytes, of extremely dilute solutions of salts and of 

 solid electrolytes, and his results have very conclusively shown 

 that the initial capacity of polarisation (K) is independent of 

 the direction of the polarising current. When a platinum elec- 

 trode has been immersed in a melted electrolyte for twenty-four 

 hours it possesses, for a given temperature, a constant initial 

 capacity of polarisation, which increases rapidly with tempera- 

 ture, while the maximum polarisation decrease!!. In the case of 

 electrodes of platinum in concentrated solutions of mos'. salts 

 (those of platinum excepted) the value of K is very neatly the 

 same for all, and varies little on account of dilution, while there 

 appears to be no connection between the value of K and the 

 specific resistance of the solution. 



A CURIOUS optical illusion is described by M. Bourdon in 

 the Kevtie Philosophique. If an object moves before our eye, 

 kept fixed, it undergoes, in passing from direct to indirect vision, 

 an obscuration, a change of coloration ; and the opposite 

 effect occurs when the object comes into the field of direct 

 vision. It is natural to suppose that this plays a part in the 

 perception of motion, and one fact proving that it does so is, that 

 if we render a slow-moving object suddenly invisible, e.g. by 

 means of a shadow, its velocity of displacement seems much 

 increased. M. Bourdon describes an arrangement in which a 

 long pendulum with white thread is swung from a cross liar on 

 a vertical support, which is illuminated from a lamp, while a 

 screen is introduced to give a shadow (the order being, obs.erver, • 

 lamp, screen, vertical support, pendulum, dark wall). The ; 

 white thread in its swing passes into the shadow of the rod and 

 screen, and each time it enters or reappears its velocity seems 

 increased considerably. It seems as if attracted into the 

 shadow, and as if it entered into the light with a sudden shock. 

 It is necessary that the thread should cease to be visible when 

 it enters the shadow. With a red thread the illusion also 

 occur.*, perhaps somewhat less vividly. A simpler plan than 

 the above is to hang a pendulum from the ceiling, shading with 

 a screen. 



A NEW method of determining the hardness, or rather perhaps 

 the friability of substances, has been described by Hr. August 

 Rosiwal at a meeting of the Vienna Academy. The measure- 

 ments consist in comparing the losses of weight sustained by the 

 bodies under investigation by scratching them with a given 

 weight of polishing material mounted on a metallic or glass base 

 until the material loses its efliciency. The polishing materials 

 used were dolomilic sand, emery, and pure corundum. The 

 diamond was assigned its place in the scale of hardness by com- 

 paring its efficiency as a polishing material with that of corundum. 

 It was found to be 140 times as hard as corundum. Tested by 

 this method, the constituents of Mohs's scale have the following 

 numerical values :— Diamond 140,000, corundum 1000, topaz 

 194, quartz 175, adularia 59-2, apatite 80, fluorspar 6-4, calcite 

 5-6, rocksalt 2-0, and talc 004. The great advantage of the 

 method consists in the ease with which the hardness of mixtures 

 of minerals in the various rocks is determined. 



