Science.

Wairarapa Standard, Volume XX, Issue 2032, 18 February 1887, Page 2 (Supplement)

Science.

Strange Thitigs Uxml Light. n?u! Kent. Lv Ibsi.u:- Ft,At:;;, There arc some things connected with the phenomena of light and In n; to which (he attention of the reader may never have been directed. Light may exist without heat, as appears in the case of phosphoric substances, which arc self-luminous. Heat may also exist without tight, but only up to a certain limit all solid substances becoming luminous when heated as highasfi77 decrees, Fahrenheit, (.'ases require a much higher degree of beat before they become incandescent. No explanation has been found of the familiar fact, that, while both the light and heat nt the sun pass unimpeded through glass, artificial heat is intercepted by this transparent medium. It is a little strange that the heat of an ordinary tire should pass freely through a layer of rock-salt, when it is unable to penetrate a pane of common glass; ami it is worth observing that while lhe but rays of the sun pass through glass with such [i- rfecl freedom, they cannot find their way back by the same channel. The warmth once inclose 1 in a hot-housc, cannot escape by the process that allowed it to enter the building ; it must first heat (he glass panesinthe roof ; as it would any oilier suhslance, in order to get out again. At ihx-l thought it is dillicult to see why the rays of the sun should pass through the atmosphere without heating it at all ; and yet. if it were not so, the temperature on the top of Mount Llanc would be higher than it is in the. valley of Chaniomrix. Lut it is still more extraordinary that the rays of the sun should pass through a cake of ice without melting it at all, as is the case when the thermom- ter stands a little above zero. That the rays of heat actually penetrate the ice is shown by the fact that a lens of iec may he used for setting lire to inflammable substances.

If it were possible for us to ti.se above tbc atmosphere which sm-romi-ls the earth, we sin m Msec no thing but an intense and sharplyilcfincd hah of finv. while every thin ii else would he wrapp -d in total darkness. There could be no «V/#VwAi« of light without an atmosphere, or some similar medium for it to act upon ; hut if the air about us extended to a height of 7On mik-s, the rays of tbc smi could not iienctrate it. and weshould be left in darkness. At l he depth of 700 feet in the ocean, the light cease# altogether, ntie-balf of the light being absorbed in passing through only seven feet of the unrest water. 1.i.-ht its-If is colourless, and therefore, strictly speaking, it is never seen. The procss by which it makes objects visible, when it falls upon them, is very interesting and wonderful, ami yet it isamatterabont which comparatively few persons ever concern llicnrelves. Why is it that in a room in which everything was absolutely destitute of colour so long as the shutters were closed, the mom-nt that (he sunlight is introduced we s- e su.-ii varieties of crimsons and greens and browns and yellow#, elaborate patterns on the walls an 1 carpeted floors and draperies and pictures of every .shade and hue .’ ‘‘That is simple enough," you may reply. When the room was dark, of course there was nothing to be seen; but as soon as it is light, everything bccurm-s visible, and each in its own special colour.” Lut why is one tiling rod and another blue This red curtain had no redness about it when the room was dark—it was .absolutely without any colour at all. It had nothing more or less but a capacity for redness, and that capacity was determined by the singular fact that when the sun’s rays fell upon the curtain it at once absorbed all but tbc red ray#, and if these were excluded from entering the room, while all the other rays were allowed admittance, there woiddnot be a red thing to bo seen, Why it certain substances absorb one set of ■Bern and other substances another sort, iPDOody can tell.

seems to be a very commonplace thing to say that the light makes objects visible by reflection ; but has the reader ever thought just what this implies? If it were possible to make a pn-Jirlly smooth surface, it would be invisible. But, as a matter of fact, nothing is perfectly smooth, and it is the little roughnesses on the surface which break up the rays of light, and thus render the object visifide to our senses. Wonderful deceptions I-! produced by the use of highly polished minors, with the most startling and magical effects.

The experiments of our modern photographers have revealed to us extraordinary chemical properties in the sun's rays, while some of these rays are entirely destitute of this peculiar power. It has also been discovered that there are rays of light outside of the solar spectrum, and which arc invisible to the human eye, just as there may be vibrations in the atmosphere too high or too low to produce an audible voice. It is a mooted question whether the sunlight falling upon an otdinary wood-flic retards the process of combustion. This is a popular notion, and its certainly looks as if the fire burned more feebly when the sun stiincs full upon it, and it is now alleged by scientific men that there may be some such influence produced by the action of the chemical rays. One would hardly have supposed that such subtle and volatile elements as light and electricity, after having been produced, could ho stored away for future use : and yet it is well known that a strip of paper, prepared after a certain fashion, and exposed for half an hour to the rays ot the sun, may be corked up and, if kept in the dark, retain its luminousness for a considerable period of time. The same property may be imparted to paint, and it has boon proposed to apply this to practical uses. What a weird look one of our country villages would iiave on a dark night if all the houses were painted with this phosphorescent pigment 1

The expensive and contractile power of heat and cold ia one of the most irresistible forces of nature. Bunker-Hill monument ia Hdl feet high, built of solid granite, and every day it oscillates to and fro, as the heat of the sun expands the eastern and western sides. If the iron rails on our roads were not allowed free play at the ends, they would curl up like a snake. The tall and massive walls of stone buildings, when they have fallen away from the perpendicular, are righted and restored to their proper position by connecting tbem with metallic rods, which) after they have been expanded by heat, in the process of cooling draw the wails together with an irresistible force. Wo arc all familiar with the application of the same principle in the hooping of oil-casks, and Die tiring of wheels. It is one of the anomalies of nature, that, while (he cold contracts every other substance, water -although it also contracts up to a certain point—is actually expanded by freezing. This is one of the most striking indications of a wise and honelieent provision, as it is all that prevents our ponds and rivers from freezing solid to the bottom. To show the power of this expansive force, 1 would mention that a brass sphere, one foot in diameter, has been torn asunder by the expansion of a cubic inch of water, inclosed in the centre and then frozen. It is a familiar and yet it always strikes us as a marvellous fact, that worlds may have been for years in existence, the light of which has not yet had time to reach our earth, and that we may still continue to see the light of stars that have been for a long time extinct.

Wind i- to lie Ibe destiny of our world, after the .-••tues of light and heal arc exhausted, a-, of necessity in proves 1 of time they must be .' Th-- earth may be very old, tun as it bad a bcginm'ii'g, -o it must, sooner or later, have an cud.