Fig. 92.
142. Sir James Clark’s Ozone Cage (fig. 92), consists of two cylinders of very fine wire gauze, one fitting into the other; the wire gauze being of such a fineness as to permit the free ingress of air, at the same time that it shuts out all light that would act injuriously on the test-paper, which is suspended by a clip or hook attached to the upper part of the inner cylinder.
143. Distribution and Effects of Ozone.—Mr. Glaisher has found that “the amount of ozone at stations of low elevation is small; at stations of high elevation, it is almost always present; and at other and intermediate stations, it is generally so. The presence and amount of ozone would seem to be graduated by the elevation, and to increase from the lowest to the highest ground. The amount of ozone is less in towns than in the open country at the same elevation; and less at inland than at sea-side stations.” It seems to abound most with winds from the sea, and to be most prevalent where the air is considered the purest and most salubrious. This may seem, says Admiral FitzRoy, in The Weather Book, to point to a connection between ozone and chlorine gas, which is in and over sea-water, and which must be brought by any wind that blows from the sea. It prevails more over the ocean and near it than over land, especially land remote from the sea; and, says the Admiral, it affects the gastric juice, improves digestion, and has a tanning effect. Dr. Daubeny, in his Lectures on Climate, writes: “Its presence must have a sensible influence upon the purity of the air, by removing from it fœtid and injurious organic effluvia. It is also quite possible that ozone may play an important part in regulating the functions of the vegetable kingdom likewise; and although it would be premature at present to speculate upon its specific office, yet, for this reason alone, it may be well to note the fact of its frequency, in conjunction with the different phases which vegetation assumes, persuaded that no principle can be generally diffused throughout nature, as appears to be the case, with this, without having some important and appropriate use assigned for it to fulfil.”
144. Registering Ozonometer.—Dr. E. Lancaster has contrived an ozonometer, the object of which is to secure the constant registration of ozone, so that the varying quantities present in the atmosphere may be detected and registered. For this purpose, an inch of ozone paper passes in each hour, by clock-work, beneath an opening in the cover of the instrument.
CHAPTER XVI.
INSTRUMENTS NOT DESCRIBED IN THE PRECEDING CHAPTERS.
145. Chemical Weather Glass.—This curious instrument appears to have been invented more than a hundred years ago, but the original maker is not known. It is simply a glass vial about ten inches long and three quarters of an inch in diameter, which is nearly filled, and hermetically sealed, with the following mixture:—Two drachms of camphor, half a drachm of nitrate of potassium, half a drachm of chlorate of ammonium, dissolved in about two fluid ounces of absolute alcohol mixed with two ounces of distilled water. All the ingredients should be as pure as possible, and each vial filled separately. When the instruments are made in numbers and filled from a common mixture, some get more than the due proportion of the solid ingredients, and consequently such glasses do not exhibit that uniformity of appearance and changes, that undoubtedly should accompany similar influencing circumstances. It is in consequence of a want of precision and fixed principle of manufacture, that these interesting instruments are not properly appreciated, and more generally used.