THE GARDEN. (By Hortus.) [Hortus is willing to answer any questions. Correspondents must give their real names and addresses, though not for publication.] A STUDY OF CLIMATE. How Warm and Cold Belts are Attained.

Te Aroha News, Volume VI, Issue 364, 1 May 1889, Page 6

THE GARDEN. (By Hortus.) [Hortus is willing to answer any questions. Correspondents must give their real names and addresses, though not for publication.] A STUDY OF CLIMATE. How Warm and Cold Belts are Attained.

The oxistence of warm and cold belts, or places subject to or exempt from frosts, has been known from time immomorial ; bub with the imperfect knowledge of atmospheric phenomena in former times the reasons for such differences were obscure. The United States Agricultural Department published several articles on the subject twenty years ago, and occasionally an intelligent farmer has given tho subject careful thought), and can explain on scientific principles some of the causes that make ono location more frosty than another, but much confusion prevails a.-, to what causes a warm bell. Many ridicule tho whole idea as preposterous, a dovice to soli land to unsophisticated people. The consideration of some of the probable causes may not como amiss. Perhaps the source of most atmospheric phenomena may be found in tho fact that heat rarities the air, causing an upward movement, the vacuum caused thereby being filled by colder ah' rushing in to take its place. In this way thei-e is a continual ascension at the torrid zone and a movement from the poles of tho earth to take its place. This continued movement of air is modified by the rotation of the caith on itt> axis from west to cast, thid motion causing a deflection of the wind from a direct course ; hence the prevailing northwest wind. This again is modified by tho annual movement of the sun between the tropics, causing summer and winter. To these phenomena are due cyclones, hurricanes and destructive storms, a* well as the refreshing rains which fertilise the earth and make it habitable. The refraction of the heated air also affects the atmosphere more or less in all | localities. The San Joaquin and Sacramento valleys, being exposed to the full action of the sun's rays, are the sources of a vast column of ascending air, the vacuum being supplied from the cooler air of the ocean which flows through the gaps of the Coast Range and even over the mountains ; hence the sea breezes during the summer months. All are familiar with the strong winds prevailing through the Golden Gate, the Ptijaro and Santa Cruz gaps, and also through the Livcrmore, Pacheco and Corral Hollow passes. Another matter to be considered is that a rarified or attenuated atmosphere intercepts and retains less of the heat of the sun's rays than when dense ; hence the -atmosphere of the mountains and the valleys is continually interchanging places, even when no wind is perceptible. The movement goes on night and day, stronger after sunset i han before. Those who travel much among mountains after sunset have noticed this phenomenon. The temperature of a country is also affected by the vicinity of large bodies of water, which absorb heat during tke day and radiate it after nightfall. Those who camp in the mountains during the summer are careful to locate near a lake, so as to avoid the frosts of the hills around. The eastern shores of Lake Michigan and also Lake Eiie are favourite places for fruifc growing, because the lakes radiate heat during the night, the prevailing winds carrying the warmer air easterly, exempting the land from tho frosts which prevail on the western side of the lakes. Those who live near the shores of the bay of San Francisco find some exemption from the frosts which prevail a few miles away. Large surfaces covered with snow intensify this constant change of air, and consequently increase the differences between the night and day temperatures. However hot the temperature of the valleys and plains along the foothills of the Sierra Nevada, night always brings a cool atmosphere, which pometimes pcimits a destructive frost. The coast ranges of mountains have no such sources of cold air, though the redwood mountains exert some influence in this way. The configuration of the earth, perhaps more than anything else, determines th<* difference of a lew degrees of the thermometer, which means frost or no frost. The well established fact that cold air is the heavio&l is the potent factor. The cold air will settle in depressions, making a kind of pond. It will not of course have as well defined boundaries as a lake of water. Some of tho sites of the ancient glacial lakes, having deep depressions and narrow outlets, have a variation occasionally of nearly 70 decrees between night and day temperature ; frost in the morning and the thermometer at 100 at noon. The towns of Jackson, Sutter Creek and Volcano are in .such depressions and consequently exposed to severe f"osts, while Mokelumne Hill, as its name implies, occupies an elevated position, and is therefore exempt from the accumulation of frosty air. A number of depressions coming together atone point, or in onelake, as at Volcano and Jackson, increase the liability to untimely frosts, as the accumulation of cold air is more rapid. The height of adjoining mountains, whether reaching to a snow elevation or not, often determines the night temperature in these valleys as to frosts or no frosts, bub adjoining elevations always influence the temperature. Every observing man has noticed the change of temperature in passing from hill to hill through deep hollows. Sometimes it is like taking a plunge bath. The writer well recollects a cold douche of that kind on a road that he had to tread after, nightfall. These cold depressions are so well known that nearly every person in selecting a building site will choose an elevation if possible. When none is attainable an upper storey is selected for sleeping rooms. The?e cold or frost ponds may be produced by groves of trees, which prevent the free movement of the cold air. The writer knows of a place with only low hills, scarcely perceptible, acting as a dam to the cold air with sufficient effect to cut down all young orange trees, while half a-mileaway oranges escape. As the pond must necessarily be shallow, it is probable that the trees would escape the frost if they could be protected until they got above the frost belt, which cannot be more than six feet deep. Heru it may be observed that the ordinary en timely frost pond is not more than five to ten feet deep. The grapevines on a trellis, or running over a tree top, will escape, while the lower ones are killed. The boundaries of these cold air lakes, not always frost lines, may often be detected by the smoke of chimneys, which rises through the dense cold air until it attains an equilibrium, when it spreads out on a level. Physicians are of the opinion that in malarial regions the sickly neighbourhood is on the shores of these cold air lakes. Many things may interfere with these deposits of cold air, even when the shape of the earth favours them. A 3trong wind will break them up ; a body of water, radiating heat absorbed during the day, will modify them ; and sometimes a spring, by causing a damp atmosphere and condensation into a fog, will savequicoan area from frost. A series of springs, having their

sources in a deep mountain, will often keep the ground' warm and save it from a frost. Clouds and fogs often protect a large extent of country. ''■ A clear, still, frosty night" is proverbial. , Applying these principles to the county of Siinta Clara, and without specifying particularly favourable or unfavourable places, a few general conclusions may be in order. Deep valleys with narrow outlets are generally frosty. The frost belt in the valley generally is confined to the lower level ; those who arc 100 to 200 feet above tide water generally escape. Wherever these frost ponds exist something may be done to avert the e/Teotb of irosts by planting trees where the rays of the morning 1 sun will not fall upon the frost-affected vegetation. This article would not be complete if the influence of the oceanic air was omitted. Santa Clara valley lies between two ranges of the coast mountains. Though usually a strong breeze descends into the valley, a still stronger one passes over it, above the mountains. This has the general effect ot breaking up a cold lake, though as there are no snowy mountains on either side the temperature never goes as low as at the foothills of the Sierra Nevada mountains, 1 and by reason of the same breeze, never attains as great a height. All precautions against frost, whether in avoiding a frost pond, intercepting the rays of the morning sun, etc., are ineffective when a north wind prevails tor some days, driving the local atmosphere away and substituting that from the North Pole. In such cases even tavoured climates do not avail. In the year 1000 such a' frozen visitor killed all tho orange trees along the Mediterranean. Florida had such a visitor a year ago. When such a disaster occurs we must begin our work anew. This part of the subject is well worth further conpiderauon, a3 by reason of the shape of the, coast, intervening mountain ranges, prevalence of winds and other things, each part of California has a different climate, varying as to rainfall, mean annual temperature, summer and winter vaiiations. etc. San Diego has a different climate from Los Angeles ; that also differs from that of Santa Barbara. San Luis Obispo, Monterey, San Francisco and Mendocino differ from each as do the counties adjoining them. Santa Clara county has its advantages, which will be described in another article.—" San Jose Herald."