SCIENCE NOTES.

Otago Witness, Issue 2362, 1 June 1899, Page 54

SCIENCE NOTES.

— In the March issue of the Photo■graphische Rundschau is to be found a communication from Dr Gebhardt, in which it is pointed out that by reason of the Opacity of the magnesium flame, only the outside is useful, and he discusses various methods for extending the area of the flame when an explosive mixture containing magnesium is to be used. Most of the methods considered — as, for example, ranging the mixture m a long line — would so •far lengthen the time of the flash as to render it useless for portraiture. The greatest success in extending the area of the flame without lengthening the duration of the combustion was realised by kindling the pile from inside, as, for example, with a cap or electric fuse. Under these circumstances the powder is so thrown about that a large flame results. In practice, the best arrangement proved to be a small pistol with large bore, and the old-fashioned cop-per-cap ignition. Half to one gramme of a mixture of one part of very finely-pow-rlered magnesium 'with three of permanganate of potassium forms the ordinary charge; but this charge would be loose in the barrel, and not confined with a wad. A long skittle-shaped flame is produced ; but this arrangement, excellent asit is from the points of view of illumination and ripidity of combustion, is subject to the disadvantage of causing a, moderately loud rsport. The desirability of using the smallest possible quantity of magnesium is not so much a question of economising the cost of the metal, as of reducing the smoke to a niinimuitt,.

— In an interesting paper recently published on the value of sugar as a food compared with fat, M. Auguste Chanveau maintains that its nutritive value is considerablyhigher than that deduced from its heat of combustion, and that the calculation that 0.7561b of the former is equal to lib of the latter is in many cases exceeded. The increase in relative nutritive value is due largely to the fact that sugar promotes assimilation of the proteids and reduces dissimilation, and the value of a food must necessarily depend not only upon the energy it is capable of supplying, but also on the direct influence it is capable of exerting in the renewal and formation of animal tissue. From whatever point of view the matter is regarded, the superiority of sugar over fat as a food, whether for men at rest or at work, is very distinct, and this is of the greatest importance in a country like England, where are the largest consumers per heiKl of population of am^ country in the world, due in a great measure, no doubt, to its being cheaper than in any other civilised country. — Lips and Character. — Physiognomists have told us that coarse, thick lips are a sign of animalism in a man ; whereas fine, thin lips are the mark of a high and sensitive nature. But, according to an eminent Geiman anthropologist, this test is very misleading, and will not bear serious examination. To begin with, there are no really thick lips amongst the white races, unless they occur by way of anomaly or freak. And if it were proved that thick lip* were the mark of some low strain in the white race, we could not affirm that any individual in whom they appeared had a coarse nature, because he might have inherited the lips from one parent, and a high soul from another. The white races are now so intermingled that physiognomical traits of this kind are very deceitful. We can only judge of the real character of a person by his general expression, or, better still, by instinct and actual experience. — Professor H. D. Steams, in the United Slates Monthly Weather Review, finds that in the British Isles and various parts of the world the percentage of winter thunderstorms decreases in passing from the coast inland in the general direction of the prevailing cyclone*. This agrees with the inference of "Professor yon Bezold that both winter and night thunderstorms as compared with summer and afternoon thunderstorms are more frequent on. coasts and the sea than inland, except perhaps where the paths of cyclones are generally from land to sea. — The most ancient method of making

ice Js practised in India,

Holes are made in

the ground, dry straw is put at the bottom of these, and on it, at the close of the dav^ axe jjlaced 0004 oi water, which are

left until 'the next morning, when the ice that is found within the pan is collected. This industry is carried on only in districts where the ground is dry and will readily absorb the vapour given from the water in the pans. The freezing, of course, is due to the great amount of heat absorbed by the vapour in passing from its liquid to its gaseous form. Another process was practised in the days of ancient Rome, when the wealthy are said to have had their wines cooled by having the bottles placed in water into which saltpetre was thrown, the bottles being the while rotated. Dr Cullen, in 1755, discovered that the evaporation of water could be facilitated by the removal of the pressure of the atmos-

phere, and that by doing this water could be frozen. Nairn, in 1777, discovered that sulphuric acid would absorb the vapour of water if placed in a second vessel separate from that containing the water, but connecting with it. This discovery he put to use in 1810 by constructing an apparatus for absorbing the vapour of water that it was desired to cool or freeze. This apparatus greatly facilitated the freezing operations of a vacuum freezing machine. James Perkins was the father of what is now known as the compression system, having invented the first machine of the kind in 1834, and as these machines, improved, are at the present day more in use than any other, a description of Perkins's patent may be of interest. His apparatus consisted of an insulated vessel in which was inclosed a second vessel containing ether ; a vapour pump ; a worm and a worm tube ; a tube between the second vessel and the pump, another between the pump and the worm, a third between the worm and the bottom of the ether vessel, and the necessary valves. As afterward constructed, the apparatus was made up of a jacketed pan, within which was the water to be cooled ; an insulated box, in which was placed the pan ; a pump to extract the vapour from the jacket; a worm in which the vapour was condensed after it left the pump ; a worm tube containing cold water to cool the worm, and by means of the latter the vapour within it ; and pipes connecting the top of the pan^ jacket to the pump, the pump with the upper end of the worm, and the lower end of the worm with the under side of the pan jacket. The refrigerating agent used with this apparatus was one derived from the destructive distillation of caoutchouc. James Harrison improved upon Jacob Perkins's patent m 1856, and it has been further improved by many others since. — " According to M. I. Holl Schooling, of Brussels," says Cosmos, "there is an old 'rule for finding the length of a man's life if the present age lies between 12 and 86. • This is the rule : Substract the " present; age from 86, and divide the remainder by 2; the result will give the number of years you have yet to live. This old rule was discovered by the mathematician De Moivre, who emigrated to England from France in 1865, and became a member of the Royal Society. The curves given by M. Schooling are interesting to examine. A first diagram shows the chance that every man has of living one year longer than his present age. At birth, this chance is sto 1; at five years, 119 to 1; at 10, 512 to 1; at 15, 347 ; at 20, 207 ; at 25, 156 ; at 30, 120 ; at 35, 97 ; at 40, 78, etc. M. Schooling affirms from his calculations that of 1000 individuals of 60 years 599 will live to be 70, 120 to 80 years, and 17 to be 90 ; while of 1000 nonagenarians, 4 will reach their 100 th year. We may add that for men of 65, the average expectation of life is 10 1-3 years."

— ■ The committee appointed by the Society of Arts to inquire into the requisite conditions of safety in acetylene gas generators have issued their report, which is based on a series of tests that were carried out at the Imperial Institute last summer. These tests, they say, " have clearly demonstrated that many types of acetylene gas apparatus can be so constructed as, with ordinary precaution, to be absolutely safe, and that lighting by acetylene need be no more fraught with danger than are any of the other forms of artificial lighting in general use." A point of considerable interest is the volume of gas jvroduced per pound of carbide used in each generator, though it does not follow that thegenerator which j'ields the largest amount of gas is necessarily the best. This factor is held, however, "to be a most important one in the choice of any apparatus. Though the gas may be safely generated in a proper apparatus outside the building to be lighted, the committee issue the warning that the generation within the house is not unattended with danger, except in experienced hands. As regards cycle and carriage lamps, which require only .small charges of carbide, they consider that very great care is required in their manipulation.