OZONOMETEI(, an instrument for measuring the quantity of ozone contained in the atmosphere. The only means of ascertaining the presence and quantity of this agent in the atmosphere, is founded upon the known action of ozone in decomposing iodide of potassium. If this salt be exposed to the action of au atmosphere coutainiug ozone, the latter unites with the potassium, forming oxide of potassium or potash, whilst the iodine is set free. In order to render this test obvious, the iodide of potassium is mixed with starch, and the iodine, when it is set free, unites with the starch, the existence of which is immediately ascertained by its blue colour: it is right, however, to add that the sufficiency of tho test is not unquestioned. [Ozone] SchOnbein, who originally described ozone, proposed this test and made use of it, by saturating paper with a solution of iodide of potas sium and starch. An the result of using this paper was to indicate the quantity of ozone in the atmosphere by the intensity of the blue colour produced on the test paper, it was necessary for comparison to use the same test paper ; hence Schiinbein undertook to supply this paper from his own laboratory, and pieces of paper for every day in the year are sold in boxes under the name " Sehiinbein's ozone test paper." In this country Mr. Motlhtt has distinguished himself by his researches In atmospheric ozone, and he also prepares a paper for supplying those who wish to measure the presence of ozone in the atmosphere. With these papers a scale of colour is supplied, each shade of colour showing the action of the ozone on the iodide and starch being marked from 0 to 10. In using this paper a slip is taken and exposed is some place to which the air has access, and there it is left for twenty-four hours. At the end of this time the paper is compared with the scale, and according to the intensity of its colour it is marked from 0 to 10.
Although this method indicates the existence of ozone at some time within the twenty-four hours, it fails to indicate the exact time at which the ozone was present, and prevents also any accurate comparison with other meteorological phenomena, as heat, wind, moisture, &a. In order to render the registration of ozone more accurate, Dr. Lankester has invented an ozonometer,-by which a strip of ozone piper 21 inches in length is exposed successively for an hour to the action of the atmosphere. In this way the ozone of each hour can be
indicated, and the sum of its effect on the paper more easily ascer tained. Dr. Lankester's instrument consists of a box (fig. 1) : the brass, dd, is down, it covers the whole box except a small space, e a, one inch in length and half an inch in width, which is cut in the lid, and through this the paper a is exposed to the action of tho air. Thu strip, after this exposure, is =tied from the cylinders cc to the wheel e, on which it is wound up. The machinery which moves the wheels is precisely similar to that of a clock, and the instrument is wound up in the same way. The following table will illustrate the method of registering the intensity of the ozone by this instrument :— iodised paper a a a is first carried round the wheel b, and passed on to the two cylinders cc. When the lid of the box, which is made of The results of ozonometric experiments show that ozone is seldom present in the atmosphere of great cities. It is generally present in air coming from the ocean, and in rural and mountainous districts, where the air is free from the contamination of animal and vegetable matter. On the sea-coast of Great Britain it appears to be more abundantly present than away from the sea. It has also been observed in larger quantities on the southern and eastern coasts of England when the wind blows from the south, or west, or south-west. As the wind veers from west to north, or from south to east, it diminishes.
the tennis or thin letter of the labial series. For the various symbols employed to denote this letter see ALPHARET. This letter is interchangeable With those which belong to the same organ, that is the lips, and with some others. Thus, 1. P is convertible with a b. The Latin, like the Welsh, was fond of the thin letters, in consequence of which there are very few words in that language which begin with b, while those commencing with p form a numerous class. It will often be found that the p in Latin words becomes a b in the related languages. Thus apicula, the diminu tive of apis, a bee, is in French abcille ; septem is in German sieben. The German language often confounds b and p, more particularly when the former is final Perhaps, too, even in Latin, the written b was pro nounced as a p in the prepositions ab, tub, ob, which correspond to the Greek awo, tiro, era.