SCIENCE NOTES.

Otago Witness, Issue 1959, 10 September 1891, Page 41

SCIENCE NOTES.

— A wide field of adaptation should suggest itself to the ingenious and skilful in connection with the mirror described in a recent issue of La Nature This is a platinum mirror which has the peculiar property of both transmitting and reflecting light. Behind the mirror is placed a movable panel or shutter, and between this panel and the glass a picture or photograph. When the panel is opened the reflection disappears, and the picture or photograph appears. These platinum minors may be used for other pnrposes. Placed in the panels of doors they will light up a corridor or a gloomy room, and on the other side they form mirrors, so that, standing on the reverse side — that is, the platinised side — one can see through the glass without being seen, La Nature gives the formula for the preparation of platinum solution.

— Inanarticleheaded"How Ice is Formed," the Pittsburg Despatch says:— "A person who has never observed the operation of Nature's great ice factory will be surprised to find how interesting it is. You need not go outside of a comfortably heated room to do this. Just place a pan of water on the window Bill, when the temperature is below the freezing point, and you will soon see something that cannot fail to interest you. If you happen to have a magnifying glass, a single lense, so much the better, for the magnifying power will reveal much of the delicate work of ice-making that is invisible to the naked eye. Anyway, as you closely watch the surface of the water you will see tiny little lances, very beautiful when seen under the microscope, shooting hither aad thither on the surface of the water. If it is cold enough to make ice in the sunlight the crystal lances will glow with all the colours of the rainbow, and, as they dart about, the rapid changes of colour will remind you of the wonders of th 6 kaleidoscope. As the water continues to chill, the little lances come together, andthen smaller and still more delicate crystals will be seen forming between the lances and welding them together. This process goe3 on until the surface is covered with a. beautiful film of ice hardly strong enough to bear the weight of a mosquito. But the process goes on under this superficial layer, and a smooth and solid surface is the result. Water is affected by changes of temperature differently from all other liquids. It seems to be a natural law for all liquids to expand in proportion to their increase in temperature, but there is a strong exception to this rule in the case of water. For example, take a quantity of water when exactly at the freezing point, 32deg above zero, and place it over a fire. As the temperature rises the volume will contract, contrary to the rule,, until the water is about 7deg warmer than it was at the beginning of the experiment. At that point, however, there is a sudden change. Contraction ceases, expansion begins, and the volume increases until the water is converted into steam."

— " When earth wasjyoung," says Dr Ball, Astronomer Royal for Ireland, "it spun around at such a rate that the day was only three hours long. The earth was liquid then, and, as it revolved at that fearful speed, the sun caused ever increasing tides upon its surface until at last it burst in two. The smaller part became the moou, which has been going round the earth ever since at an increasing distance. The influence of the moon now raises tides on the earth, and, while there was any liquid to operate on in the moon, the earth heaped up much greater lunar tides."

— The study of crystals (writes a B. Sc. in the Adelaide Observer) is becoming of more importance every year in geology, for there are many questions in the history of rocks that the broad old methods throw no light on. A whole new department of geology has been opened by the application of the microscope to the examination of thin sections of rock, and the characters of such sections depend mostly on the nature of the crystals of its constituents. Professor Judd, one of the leading workers in the new branch of geology, delivered a most interesting lecture recently on the power possessed by crystals of renewing their youth. Crystals can resume their growth after any time ; if mutilated they can repair their injuries when given a chance to grow. Crystals of two distinct substances can intergrow amongst one another, each remaining true to its own form. These properties of crystals go to explain many peculiarities in rock structure. Quartz crystals have been found that after a few million years of grinding and rubbing down they have been placed in circumstances again favourable to growth, and have coated themselves afresh with clear sharp crystal ; and similarly in whole rock masses processes of crystal decay and growth have alternated with varying geological conditions. None but those engaged in the work can have any idea of the patience required in the microscopic study of rocks, especially in the pioneering part of the work. Now there are signs that progress will be more rapid, as the methods of prepaiation and examination have been elaborated.

— Iridium is a white metal, almosb as hard as the ruby, brittle at ordinary temperature, slightly malleable at a white heat. Its specific gravity is 22*3, being the heaviest known metal, while it is also the most infusible, requiring the intensest heat of the oxy-hydrogen blowpipe to fuse it. Softening begins at about 2200deg Cent., and it is melted at a temperature between 2300deg and 2400deg Cent. It is specially used for the points of gold pens, as it is practically indestructible, and is not affected by any acids. It is also used in wire drawing for the production of fine gold and silver threads, taking the place of the ruby, and in the construction of the knife edges of delicate balances it advantageously replaces the agate which is commonly used, permitting the use of much finer edges, and conse-

quent increase of sensibility. The great resistance it offers to heat has given rise to the idea of using it in electric crayons, the points of which, if formed of it, would be practically indestructible. In combination with osmium, itisfoundasiridosmine, and also in combination with platinum, in the Urals, California, Canada, "South America, East Indies, Borneo, and Australia.

— The romance of science probably embraces no more striking story than the oftcited history of coal tar. From this troublesome waste of a few years ago, according to Professor R, Mendola, about 300 colouring matters are now made, 30 of them being fast dyes of general utility, and 30 more fast enough for all practical requirements. The value of the coal tar colours annually produced in Great Britain and on the Continent has reached some £5,000,000. From the same original source are also derived such explosives as picric acid, medicines such as antipyriD, sweets such as saccharin, and perfumes, resembling vanilla, bitter almonds, &c, not to mention hydroquinon and eikonogen, used by photographers and others.