Page:Popular Science Monthly Volume 82.djvu/282

278 Nevertheless, their use has not spread since they were proposed, two or three years ago. It is to be hoped that they are not destined to share the oblivion of some analogous terms relating to atmospheric pressure proposed about forty years ago by Prestel; viz., "pleiobar," "mesobar" and "meiobar."

Purely English terminology has received some useful amendments at the hands of Dr. Hugh Robert Mill, who in this respect is carrying on the worthv traditions of "British Rainfall." Thus he has balanced Symons's terminology of droughts—the "absolute" and the "partial" drought—by introducing the term "rain spell" for a period of more than 14 successive days with rain. This expression, however, like the term "rain day," is one that would need to be redefined in other countries. Dr. Mill has rendered an even more useful service to precise terminology by distinguishing between the words "mean," "average" and "general." He speaks, for example, of the mean temperature at Camden Square during the month of June, 1900; the average temperature at the same place in June during a ten-year period; the general rainfall over the whole county of London in May, 1910, and the average general rainfall over the same region for a term of years.

British meteorologists have also succeeded in establishing a working terminology in English for the various deposits of frozen moisture that have occasioned so much fruitless discussion at international meteorological meetings. The Meteorological Office now applies the term "rime" to the rough deposits due to fog, and "glazed frost" to the transparent smooth coating usually caused by rain which freezes as it reaches terrestrial objects. The ambiguous expression "silver thaw" has been discarded in British meteorology.

The endless subject of cloud terminology and nomenclature can not be discussed in this paper; but I wish to call attention to one term in this connection recently introduced by M. Besson. This is the name "nephometer" for an instrument used in measuring the amount of cloudiness, as distinguished from the familiar "nephoscope," by which we observe the positions and movements of individual clouds.

German meteorologists have lately introduced the all-Greek names "chionometer" and "chionograph," and the hybrid "nivometer," for the instruments used in measuring snow. Although these terms will hardly displace "snow-gage" in English, we shall probably find it convenient to use their derivatives; e. g., "nivometric"; just as we use "pluviometric," though we generally avoid "pluviometer."

The name "ceraunograph" applied by Odenbach in 1891 to his variety of the thunderstorm-recorder now seems destined to become the generic and international designation for the numerous instruments of this class. Particular forms have been known as "thunderstorm-recorders," "lightning-recorders," "brontometers," "brontographs," "ceraunometers," "electroradiographs," etc. "Ceraunophone" will.