The Nature Column.

Digger (Invercargill RSA), Issue 27, 17 September 1920, Page 12

The Nature Column.

(By "Student.")

("Student" will be plcsed to receive notes on any braraeh of Natural History. Observations on birds, insects, plants, etc., will be equally welcome. If using a pen-name, will correspondents please enclose real name and address. ) Recent flies from England show that science is makiri g some very great strides, An attempt is now bein.g made to further the interest in science of all reasonably well educated people. Excellent articles by scientists of note written in non-teeh-nical language, are now revealing the latest advances ih scientific though t. One of the latest discoveries is in connection with the structure of crystals. A large number of the substance3 with which we come into contact in our daily life, are crystalline in structure. The crystals of such substances as salt and sugar are easily seen, while those in steel require a microscope. The rocks are inostiy crystalline, and from the shape of the crystals we can determine the kind of rock, and even give a fairly accurate statement of the chemical constitucuts. 'ihe angle at which two face of a crystal meet is always the same for a part.icular mineral. Many crystals also have the property of splitting or cleaving in a certain direetion or directions. It has heen supposed that the above, properties of crystals are caused by the way in which the molecules composing them are built up, or arranged. We now have proof of this, with the most powerful microscope we cannot see anything much smaller than a particle one thousand times as large as a molecule. This is not beoause we cannot make better microscopes, but because particles of matter, smaller than the wave length of light, scatter the light and do not refiect it so as to form an iu.iage. It was necessary to find somethirg that would take the place of ordinary light. X Rays have many of the attrilmtes of light. They travel at the raio of 186,000 miles per second. This is the sanie rate- as l%ht, heat and wireless waves. Wireless waves are slow vibrations, heat and light are quicker and X Rays are very much faster. By transmit. firig the rays through a ci'ystal on to a photographic plate, it has been possible to get patterns showing a diffraction grating as a plate rulecl with from 10,000 t.o 20,000 lines to the inch and is used to show interference between light waves. , A nnmber of models have been made to illustrate the way in which crystals are built from molecules, showing the characteristic angles and cleavages. The age ' of the earth is another oue of these pereUnial questions' which occupy the minds of scientific men. Evolution demands a long period of many millions of years to bring life to the state in which it is to-day. Many methods have been devised for the purpose of estimating the age of the earth such as : the loss of heat from the incandescent stagc to the present. Calculation of the time necessary to lay down the thickness -of sedimentary rocks at the present day rate of deposition. Estimates have heen made on the basis of the amount of salt present in the sea. Lord Kelvin in his fmal estimate based on the loss of heat, gave the age of the Earth at 20 million years. Other investigators working on the other methods go up to 300 million years. Biologists would not hear of Lord Kelvin' s estimate, and for many years the source of error in his ealeulations was sought for. The appearance of Radium solved the difficulty. Radio-active substances have been found in such quantity that the physicists are embarrassed to account for the fact that the Earth does not grow hotter. For if the sanie conditions applied tlirapomhtis the met.mr dthe shadsm hth throughout, this world should grow hotter. However the explanation seems to be that the radio-active luaterials are only present in quantity in the crust. It has been found that the elements Uranium Thorium gradually break down through radio- ' activity until they finally become lead. The fate of breaking down has been determined and measurements of the products of decomposition found in the rocks* give a fair estimate of the age of the rock eoncerned. By this nreans it has been estimated that the age oi our globe is more than 1,600 million years. The above metbod of estimating the age of rocks is going to be of considerable use to the geologist. It enables him to make comparisons of the age of those rocks comprising the pre-Cambrian period. These rocks have little or no definite time inarks, though they comprise about half of the strata since the beginning down fo the present. The Tertiary period is put down at 70 million yeara and biologists have'plenty of time to account for the diversified forms of life now to be found.