March 1st, 1SS7.] 



SCIENTIFIC NEWS. 



21 



ohms simply wound with cotton on a rainy day proved 

 worse than all others examined, but exhibited no trace of 

 polarisation after having been baked at 150° C (300" Fah- 

 renheit), or again after having been paraffined. Ten days 

 afterwards, however, the polarisation reappeared ; and a 

 drop of water put on the coil increased it to its former 

 maximum within five minutes. The polarisation appears 

 thus to be due to the electrolysis of the moisture absorbed 

 from the atmosphere. For very accurate resistance coils, 

 the ordinary paraffin insulation would not be safe ; and Mr. 

 Thomas recommends either to fill the space about the coil 

 entirely with paraffin, or to employ impervious boxes filled 

 with a suitable petroleum. 



Higher Explosives for Artillery. — The enormous 

 power of the higher explosives, of which dynamite is the 

 best known, has ever been looked on with longing eyes by 

 that ingenious and very numerous class of persons who 

 devise new methods of human destruction. Up to recent 

 times, however, higher explosives have proved a very ignis 

 fatuHs to the military inventor, but within the last few 

 weeks, some substantial progress is reported to have been 

 made in the United States. The Government authorities 

 of that country have established a Dynamite Board, and the 

 arguments brought forward by this body have convinced 

 Mr. Whitney, the secretary of the U.S. navy, that there is a 

 lair chance of a higher explosive than gunpowder being used 

 for the bursting charges of shells in large guns, or rather 

 long guns, for we believe some of the weapons proposed 

 are 120 to 168 calibres long. As is pretty well known, the 

 reason that the higher explosives have not been used in shells, 

 is on account of their liability to explode in the gun by the 

 concussion of the discharge. Much ingenuity has been ex 

 pended in the effort to set the projectile in motion more 

 gradually. One weapon was made, or proposed, with 

 pockets at the side to be filled with powder which would 

 explode as the projectile passed it. Another inventor de- 

 vised a buffer arrangement of india-rubber, metal springs 

 have been suggested, whilst the devices are legion in which 

 air has been proposed as a cushion. An air-gun appears, 

 however, to be the favoured device of the Dynamite Board. 

 The projectile of this weapon, which has a 125 in. bore, is to 

 contain 400 lbs. of nitro-gelatine. Three of these guns, it 

 is said, are to be mounted on one of the new cruisers now 

 being constructed for the U.S. navy. The Americans say 

 that the nitro-glycerine is twenty times more destructive 

 than the most powerful explosive that we in Europe have 

 experimented with, for the 200 lb. charge, which was that 

 originally proposed, is equal to about 2,000 lbs. of gun 

 cotton. As for the destruction that would be wrought by 

 the larger charge of 400 lbs., that, they say, is beyond 

 computation, but it is enongh for us to know that it would 

 " level an army to the ground, and kill or demoralise every 

 sailor in a fleet." In which case, it would appear, that the 

 millennium has at last arrived 



A Russian Volcano. — Not long ago the town of Baku, in 

 Southern Russia, was threatened with partial destruction by the 

 sudden outburst of a natural naphtha fountain. Now a volcano 

 of earth and hot mud has broken out about ten miles from the 

 town on the Lok Batan. The following is taken from a Times 

 telegram: — "Quite suddenly', at eleven u'clnck at night, the 

 noise of an explosion was heard, and from the summit of Lok 

 Botan there was shot up an enormous column of fire some 350 

 feet high. The whole country was instantly lit up brighter than 

 day, and the heat could be felt at nearly a mile from the crater. 

 There was scarcely any wind, so that the column continued to 

 ascend ([uite vertically. This lasted with .short intervals of s\ib- 

 sidence all through the night, and the following twenty-four 

 hours. The volume of muddy liquid thrown out was estimated 

 at half a miUion cubic sojciics — the Russian sojcnc equalling 

 seven feet — and has spread itself over more than a square mile 

 to a depth of from seven to fourteen feet." 



THE ROYAL INSTITUTION. 



SIR WILLIAM THOMSON delivered a lecture, on the 21st of 

 January last, at the Royal Institution. The subject was the 

 probable origin, the total amount, and the possible duration of the sun's 

 heat. The natural history of plants and animals within the time of 

 human history showed that there had been no exceedingly great change 

 in the intensity of the sun's heat and light during the last 3,000 years ; 

 but there might have been changes of 5 or 6 per cent. But we had 

 proof of something vastly more than 3,000 years in geological history 

 for the mere age of the sun, and evidence of continuity of life on the 

 earth probably for millions of years past. The sun had been doing work 

 at the rate of 476,000 millions of millions of millions horse-power, and 

 at possibly more than that rate, for a few million years. The explana- 

 tion of this, which possessed the highest probability, was Helmholtz's 

 form of the meteoric theory, the principle of which was that the sun's 

 initial heat was generated by the collision of masses gravitationally 

 attracted to one another from distant space to build up its present mass ; 

 and the shrinkage due to cooling gave, through the work done by the 

 mutual gravitation of all parts of the shrinking mass, the vast thermal 

 capacity, in virtue of which the cooling had been and was so slow. 

 The rate of shrinkage corresponding to the present rate of solar radi- 

 ation was 331 metres on the radius per year, or one ten-thousandth of 

 its own length on the radius per 2,000 years. Hence, if the solar 

 radiation had been about the same as at present for 200,000 years, the 

 sun's radius must have been greater by i per cent. 200,000 years .ago 

 than now. If the sun's effective thermal capacity could be maintained 

 by shrinkage till twenty million times the present year's amount of heat 

 was radi.ated away, the sun's radius would be half wh.at it is now. liut 

 the density which this would imply, being more than eleven times that 

 of water, w.as probably too great to allow the free shrinkage to be still 

 continued without obstruction through overcrowding of the molecules. 

 It seemed, therefore, most probable that we could not, for the future, 

 reckon on more of solar radiation than twenty million times the 

 amount at present radiated out in a year. Also the greatly diminished 

 radiating surface at a much lower temperature would give out 

 annually much less heat than the sun in its present condition. 

 These considerations had led Newcomb to the conclusion that it 

 was hardly likely that the sun could continue to give sufficient 

 heal to support life on the earth — such life as we were acquainted 

 with, at least— for ten millions of years from now. In these calcula- 

 tions the density of the sun had been considered as uniform for the sake 

 of simplicity. In reality, there must be a wide difference between the 

 density at the centre of the sun and the density at the surface ; but it 

 did not seem probable that the correction could add more than a few 

 million years to the past of solar heat, and what could be added to the 

 past would have to be deducted from the future. By the light of more 

 recent calculation, and taking into account all possibilities of greater 

 density in the sun's interior and of greater and less activity of radiation 

 in past ages, it would be rash to assume as probable anything more than 

 twenty million years of the sun's light in the past history of the earth, 

 or to reckon on more than live or six million years of sunlight for the 

 future. As to the early history of the sun, five or ten million years ago 

 it might have been about double its present diameter and an eighth of 

 its present mean density, but we could not with any probability of 

 argument go on continuously much beyond that time. It was impos- 

 sible to help asking, however. What was the condition of the sun's 

 matter before it came together and became hot ? It might have been 

 two cool solid masses which came into collision with the velocity due 

 to mutual gravitation, or, but with enormously less of probability, it 

 might have been two masses cominj into collision with velocities con- 

 siderably greater than those due to gravitation. If two cool solid 

 globes, each of the same mean density as the earth and of half the sun's 

 diameter, were given at rest at a distance asunder equal to twice the 

 earth's distance from the sun, they would fall together in half a year. 

 The collision would last a few hours, and in the course of it the globes 

 would be transformed into a violently agitated incandescent fluid 

 mass, with about eighteen million years' heat ready made in it, 

 and swelled out to piissibly three or four times the sun's present 

 diameter. If, instead of being initially at rest, two globes had a trans- 

 verse relative velocity of i'42 kilometres a second, they would just es- 

 cape a collision, and would revolve in equal ellipses round the centre of 

 inertia. If the initial transverse relative velocity weie a little less than 

 I -42 kilometres a second, there would be a violent grazing collision, 

 and two bright suns would come into existence in a few hours and 

 commence revolving round their common centre of inertia in long 

 elliptic orbits, the eccentricity of which would be diminished. If the 

 initial transverse component relative velocity of the two bodies were 

 just 68 metres, the moment of momentum would be just equal to that 

 of the solar system, of which 17-iSths was Jupiter's and i-iSth the 

 sun's, the other bodies of the system not being worth considering in the 

 account. Assuming the sun's mass to be composed of portions which 

 were far asunder before the sun was hot, the immediate antecedent to 

 its incandescence must have been either two bodies with details differ- 

 ing only in proportion and densities from the cases considered ; or it 

 must have been some number more than two — at the most the number 



