August 30, 1877] 



NATURE 



375 



photometer employed consists of a cardboard screen, having an 

 aperture divided into two equal portions. One half is covered 

 with tissue paper and illuminated directly from behind. Behind 

 the other half is set, at the polarising angle, a mirror of black 

 glass. Light from a second lamp falls upon a screen of tissue 

 paper, whose light is then reflected in the mirror. Thus the two 

 halves of the aperture may be illuminated equally, but with 

 light in one case wholly unpolarised ; in the other, wholly polar- 

 ised. Let two Nicol prisms be now taken, having their principal 

 sections placed parallel and perpendicular, respectively to the 

 plane of polarisation of the mirror, and let one Nicol be placed 

 in front of each eye. One eye inly will receive the whole of the 

 polarised light, while the unpolaristd will be equally distributed, 

 half to each eye. The total amount of light received upon the 

 retinal surface will be the same from each half of the aperture ; 

 but their apparent illuminations will be unequal, that of the 

 polarised light appearing the greater. By comparing the dis- 

 tances at which the lamps must be placed, it appears that light 

 is more powerful in producing an effect when concentrated upon 

 one eye than when equally distributed to the two, though accord- 

 ing to what law experiments are not yet sufficiently numerous or 

 exact to determine ; but, on the other hand, the light so concen- 

 trated on one eye does not produce the 'sensation of twice as 

 much illumination as the half of the light viewed by both eyes 

 at once. 



A paper by Mr. C. Meldrum was read On the Diurnal Varia- 

 tions of the Barometer and IVind in Mauritius. Mr. Meldrum 

 remaiked that in 1S75, 1S76, and 1877, the number of cyclones 

 had been much below the average, and that there had not bdn 

 any one great storm such as that which occurred in the perio^Is 

 1S60-63, and 1870-73. This, so far, confirms the hypothesis of 

 a connection between the frequency of sunspots and the frequency 

 of cyclones. 



With regard to the rainfall the evidence in favour of a cycle 

 corresponding; with the sunspot cycle has much increased. Dr. 

 Hunter, of Calcutta, has lately found for Madras a rainfall cycle 

 identical with that which the author had previously found both for 

 India and various other parts of the world. Mr. Meldrum has 

 recently discussed the rainfalls of thirteen stations in the French 

 colonies for various periods from 1S32 to 1872, and obtained 

 results nearly the same as those that had been found for 144 

 stations scattered over both hemispheres. Dr. Fritz, of Zurich, 

 has shov/n that the severest hailstorms and the highest levels 

 of the rivers occur on the years of maximum sunspot. In 

 short there can, he thinks, be little doubt of an eleven-year 

 rainfall cycle, and when its laws are known they will probably be 

 of much practical use. 



Account of a Meteor •which passed over Bhawnepoor, in India, 

 in October, 1873, by Major G. Noel Money. — In the beginning 

 of October, 1S73, I was staying for a few days at Bhawnepoor, 

 capital of the independent state of the same name, which is 

 situated along the left bank of the River Sutley, and north of 

 the great sandy desert of Bikaneer. 



Early one morning I was roused from ray sleep by a sound 

 exactly resembling that which would be produced by half-a- 

 dozen express trains passing close to the house at the same 

 moment. The room was as light as the brightest noonday. 

 Before I had time to collect my thoughts, two violent e.xplosions 

 in rapid succession shook the whole hou-e ; the doors and 

 windows rattled for fully ten or fifteen seconds. Earthquakes 

 being of not unusual occurrence in the north of India, particu- 

 larly at that time of the >ear, I naturally concluded this was 

 something of the kind, and hurried out of the house. As I did 

 so the light faded, and I was surprised to find, as I reached the 

 verandah, that it was still night, although the first streaks of 

 dawn were visible in the east. The native servants were running 

 out of their houses in the greatest alarm ; I asked what was tiie 

 matter. " God knows ! the sky has fallen," was the reply. 



After breakfast we heard that a shower of stones had fallen 

 eighteen miles off to the north-east of Bhawnepoor, and later 

 in the day some pieces were brought in. The largest was 

 an irregular mass, as far as I can recollect about three feet lon^, 

 and a foot thick ; still hot, blackened outside as if by the action 

 of fire, of which it smelt strongly, of a dark grey colour inside, 

 and very heavy. I have now a piece which I broke off this 

 large mass ; although no bigger than a man's fist, it weighs 

 nearly t«o pounds. The natives who brought these in said there 

 were many n:ure ; one they declared, was as large as a bullock- 

 cart, and so hot that they cjuld not touch it. 



It was afterwards ascertained that a second shower of pieces. 



apparently the result of the second explosion, fell about thirty 

 miles beyond the first. It is satisfactory to know that there was 

 scarcely a possibility of deception as regarded these pieces ; 

 there not being such a thing as a stone, rock, or pebble the size 

 of a pea, within the radius of a hundred miles from Bhawnepoor, 

 the soil being either pure alluvial deposit or the finest sand. 



The accounts given by native eye-witnesses of this meteor 

 were varied and unreliable, and one could only arrive at a satis- 

 factory result by an exhaustive process of comparison, but I was 

 fortunate cnoirgh to meet, the same day, a thoroughly trust- 

 worthy eye witness in the person of an European overseer who was 

 superintending the works at a new palace, which was in course 

 of erection for the Nawab at Bhawnepoor. This man had gone 

 down to the works before daybreak to look after a brick- kiln, 

 and being in an open space had an uninterrupted view of the 

 meteor. He described it as a large ball of fire, as big as twenty 

 moons, which passed, with a roaring sound, directly over his 

 head in a north-easterly direction. It lit up the whole sky, 'the 

 light being perfectly dazzling, and left behind it a flaming track 

 of red, green, and yellow. Before passing out of sight two 

 explosions in quick succession took place, at each of which a 

 shower of sparks seemed to fall, but no alteration appeared in 

 the size and shape of the meteor itself. 



It has always been a subject of surprise to me that no attempt 

 was made by Government to collect any information regarding 

 this meteor. Had reports been called for from the various dis- 

 tricts it would have been easy to ascertain where it was first and 

 where last seen. Some estimate might then have been made as 

 to its size and distance from the earth's surface. 



To give some idea of its magnitude, I may mention that at 

 Dera Ghazi Khan, seventy miles north of Bhawnepoor, it was 

 seen and heard nearly as plainly as it was by us. At a place 200 

 miles north and a little west of Bhawnepoor, it was so brilliant 

 that a native gentleman was, as he informed me, startled from his 

 sleep by the sudden light, and ran out of his house thinking the 

 next house must be on fire. He did not, however, hear any 

 explosion. 



Some soldiers of my regiment in Terar, in Afghanistan, 400 

 miles north of Bhawnepoor, told me that they had also seen it, 

 and that it was so unusually large and brilliant that the mooUahs 

 ( Mahomedan priests) were much exercised in mind about it, con- 

 sidering' that it must forebode some calamity. 



Very little notice was taken ot the occurrence in the local 

 papers, but this is to be accounted for by the fact that it passed 

 over the most desert and thinly populated district in the whole 

 of India. I believe, however, I am right in saying that it was 

 also seen in Ajmere and Jypore, over 400 miles to the south-east 

 of Bhawnepoor. 



On the Detcrniination of Timteratiire Coefficients for Insulating 

 Efivelopcs, by T. T. P. Bruce Warren. — At the Exeter meeting 

 of the British Association I read a paper on electrification, in 

 which I endeavoured to show that the rate of variation in the 

 insulation resistance of a core or cable under changes of tempera- 

 ture could be determined for any period of contact. A statement 

 was made in that paper which has led to the belief that india- 

 rubber has the same constant for correcting from one temperature 

 to another, and for any period of contact. 



Prof. Fleeming Jenkins, Mr. Latimer Clarke, and others have 

 pointed oat that this phenomenon is not met with in gutta percha, 

 or any other insulator with which they are acquainted. This his 

 led me to re-examine the matter, and to consider carefully the 

 experimental data upon which the paper was founded. 



The method of representing graphically the decrease of resist- 

 ance due to increase of temperature corresponding to one minute's 

 electrification, can be followed out for two, three, or any number 

 of minutes. In this w.ay a series of logarithmic curves are 

 obtained for any required duration of contact ; these curves are 

 generated by a constant which must first be ascertained by expe- 

 riment for changes of temperature at the end of one, two, three, 

 &c., minutes. 



This was omitted in the previous paper, or at least not dealt 

 with as the importance; of such a subject required. 



The phenomenon of electrification, from what has just been 

 pointed out, must appear to every electrician to have received 

 additional importance, so as no longer to be regarded as an unin- 

 telligible or inapplicable fact. One very important consequence 

 of its being reducible to an intelligible variation is that we can 

 irovv calculate not only the changes in the resistance of an insu- 

 lator due to variation of temperature, but we can ascertain with 

 the same precision any required change due to prolonged contact, 



