SCIENTIFIC.

Otago Witness, Issue 1834, 14 January 1887, Page 36

SCIENTIFIC.

' " - How Kaiu is' Produced)

Did it ever occur to the reader that the *" is jusl as much .Water in the air above him on a clear, bright day as on a cloudy or rainy one ? Rain does not come from somewhere else, nor is it wafted over you by the wind from elsewhere. The water that was over you is simply wafted on to some other place. Water'is absorbpd in tbe air above us at a certain temperature, and ifc becomes insensible. Cool that air by a wind draft of cooler atmosphere, or by electrical or chemical influences, and the moment the air becomes cooler it gives up some of the watery particles that were insensible orinvisible at the higher temperature. These small particles thus given out unite, and when enough of them coalesce, obstruct the light and show as clouds. When enough of them unite to be too heavy ro float in the air, they begin to descend; pair aftin- pair of thorn come together until a rain-drop is formed. One ot those minute rain-drops is made np of millions of infinitely small watery particles.

Air parsing over the cold tops of mountains is cooled down so that it gives np a good deal nf the concealed watery vapor, and hence little rain falls in the region along the ice side of, such mountains. This is why so little rain falis in Colorado, and in other places north and south of thai State. The prevailing winds blow from the west, and the cool tops of the Itocky Mountains lower their tumperatuio, and thus take out the moisture that would otherwise fall in rain HOW JJAINI>JIOT\S, HAIL., AXD SNOW ABB

FOK.MKD

In v paper on t ho" Formation of Rain, Hail, und Suuw,'' recently read before the Meteorological Society, by Mr A. W. Olayden, F.G.S., the author poiuts out that all observations tend to show that, except under quite abnormal conditions, the temperature o£ the atmos|)here falls as tho height above the sea, level increases : and there seems no reason whatever for assuming that the law does not apply to that portion of the atmosphere which forms a cloud., Hence, if a drop were ia be formed at or near the tipper surface of a cloud, it would 'fall down into a region saturated with vapour at- a temperature above its own. Tho result will be further condensation producing a larger drop ; and (his process will continue nntil it leaves the cloud. Jf it ft. temperature, be below ihe dew point of tho aii 1 it hills through, condensation will continue until it reaches the ground. However, it is obvious that this subsequent gain cannot bear any very lart c proportion to the growth while falling through the saturated cloud, from whicli the conclusion follows that the size of the drop must increase with the thickness of the cloud. The author suggests that condensation begins on the upper surface of the cloud by the cooling of some of the liquid cloud particles. If this particle is cold enough it will solidify, and snow will be formed. Should it not be quite cold enough to solidify at once, owing to its minuteness, but remain still below the freezing point, hail i.s formed. Finally, if the temperature is not low enough for either snow or hail, rain is produced.

Value of the Lens to Man.

Ever since man was capable of observing things around him, he mv.it often have scon that a straight stick thrust obliquely into the water appeared to ba bent, at its sinfneo. It was a long' time before man learned the value of this fact ; but at length the lens was discovered. The invention consisted simply in the form given to a piece of glass —in givmg to one or both of! the surfaces of a disk of glass" a curved form. This we know forms a lens, and a lons has become one of the most, valuable devices known to man, but it was a long time after it.s invention before it became of much value.

I alluded to spectacles as a valuable invention. I have never *ec-n any attempt to estimate its value I do not know ihat i have ever heard the inquiry made. And yet when we remember ihat nrarly every per-son above the age of 4.">, and very many below that age, use glasses, wo sec: that they in list enter largely into (ho sum of our comforts. How many person.-' would bje deprived of \he pleasures and buiu'-lils of reading- ami writingduring a large portion of their lives but for this simple invention ! How many kinds of labour would be performed badly, and with great discomfort., but for these devices ! At what disadvantage literary labour would be carried on without them ! For how many delicate handicrafts would men and women become unfitted in their later years but for them ! At what discomfort an *1 inconvenience would domestic needle-work be performed in their absence ! How much trial of the patience is saved by their use ! I doubt not our tempers are much better in old age for these helps.

But the value of the invention of the lens is not limited to its use for spectacles. From jfc has grown up those wonderful instruments, the telescope and microscope. Through the former lias come ;i largo part of our astronomical knowledge, whifiii lias a great co.nmercia.l value from ilie security it gives to man in navigating the oceans. It ha? aho a high mowil and mental value from the ftjld it opens to the..exerciso ancl training oi the powers of observation and imagination : from Ilui new conceptions it lui^'givcn us of the immensity of creation, and of tlic powei which travd it- birth.', J wonder if a,uy mtxv.

,can rise,,from a, contemplation of thesefacts,the;,mysteries, ipid' .magnitudes oi the uni-verse-revealed to 'us, by the -telescope arid spectroscope, without repeating to himself, with a , new sense of .its significance, the question : " What , is man that Thou art mindful of him, or the son of man that Thou visitest him ?"— Chauncey Smith, in Popular Science Monthly.

— Some N men give according to their means, and some according to their meanness. — The following is tokl of a dmtr-out whose love of oysters is notorious : At a dinner party one evening oysters were duly served to him ; but, when he got to the fourth, he sent his plate away. The hostess,, by whom he sat, observing this, expressed her concern, addiug, " I assure you they are natives ! " "I don't doubt it," he replied; "but that last one I ate was a settler."

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