EATS' GAUGES, ETC.] 



METEOROLOGY. 



1163 



ated glass tube. It consists of a short cylinder, twelve 

 inches in diameter, having connected with it, by means 

 of a stopcock, a glass tube graduated to hundredths, and 

 terminating in a lower vessel, which will contain a suf- 

 ficient quantity of water, to be raised by artificial pres- 

 sure into the upper one, for exposure to the atmo- 

 sphere. 



To use the apparatus, pour water into it until it rises 

 to the zero in the glass tube ; then, by means of a syringe, 

 force the air through the tube X (Fig. 73) into the lower 

 vessel, so as to raise the water into the upper one to any 

 height you please. Now shut off the stopcock beneath to 

 retain the water in the upper vessel ; then, having ex- 

 posed the apparatus for any length of time required, open 

 Fig. 73. 



the cock ; the water will run into the lower vessel, fillin<* 

 it and part of tlie glass tube, the divisions of which will 

 now indicate the quantity of water evaporated. Ne- 

 gretti'g is the cheaper instrument, being simply a cylin- 

 der of the diameter of eight inches, which fits into a 

 wooden box filled with wet sand ; this keeps the outside 

 of the metal cool, and prevents that excessive evapora- 

 tion which would result from the heating of the metal 

 by the sun. Where the diameter of the gauge is large, 

 and the water is several inches deep, the effect of the 

 sunshine on the metal sides is not felt. 



RAIN GAUGES. There are several constructions, yet 

 none so good as Negretti and Zambra's, which is simple, 

 and at the same time prevents any loss by evaporation 

 an important point, which has been too much over- 

 looked. Another contrivance is that of a cylindrical 

 vessel of brass or zinc (Fig. 74); 

 the latter would be the cheap- 

 est, and answer all purposes 

 equally well. Into this cylin- 

 der, a funnel, with its tube 

 bent, fits tightly : the diameter 

 should be eight inches, and the 

 tube about an inch in length. 

 The object of this bent tube 

 is to prevent evaporation tak- 

 ing place from the surface of 

 rain collected in the rain gauge, 

 for a few drops of water will 

 hermetically seal the opening 

 from the escape of vapour. 

 Most frequently the evening dews will deposit sufficient 

 moisture for this purpose, which the heat of the day will 

 scarcely have time to dissipate, before night brings a 

 fresh supply. 



n 



The readiest mode of measuring the amount deposited 

 in the gauge, is by procuring another cylindrical vessel, 

 or measure, which is exactly four 

 inches in diameter, and four inches g ' 



deep : this, when quite full, will 

 just contain an amount equal to the 

 deposit of an inch of rain as col- 

 lected in the eight-inch gauge. Parts 

 of an inch can be measured by 

 plunging a rule (Fig. 75) perpen- 

 dicularly to the bottom of the mea- 

 sure, the portion wetted by the 

 water being the decimal part of an 

 inch required. Having made a rule, 

 exactly four inches in length, and 9i 

 divided it into ten equal parts, and 

 each division being subdivided into 00 

 ten others, a measure is obtained 

 which will read off the hundredth of 85 

 an inch ; and, as the divisions are 

 tolerably wide, it is not difficult to 

 estimate even to thousandths of an ;5 

 inch. Thus, for example, as used 

 in the measure, the rule four inches 70 

 long, divided into 100 parts, repre- 

 sents one inch of rain fallen ; the ci 

 score at twenty-five, or one inch, 

 represents a fall of a quarter of an 

 inch, and so on. 55 



ELECTROMETERS. Atmospheric 

 electricity has been much neglected 50 

 by meteorologists ; it is an impor- 

 tant item of meteorological investi- 

 gation. There are several methods 

 of studying the subject : the most 

 simple is Glaisher's electrometer, 35 

 which, being portable, should be- 

 come generally adopted. Where 30 

 there are the conveniences for having 

 exploring wires, properly insulated, 2 ' 

 the results are more satisfactory ; .,,, ^ 

 and when this plan is adopted, the .2 

 following electrometers should be 

 used : 



1. Do Saussure's Electrometer, 

 which consists of two fine wires, each 

 terminated by a small pith ball, their 

 expansion being measured by a gra- 

 duated scale. 



2. Volta's Electrometer, consisting of two thin stems 

 of about two inches in length, and fitted to a metal rod 

 by small rings. 



3. Singer's Electrometer, consisting of two slips of 

 gold-leaf. For stronger electricity, a pair of Dutch-gold 

 leaves become a useful addition. 



4. Zamboni's Dry-pile Electrometer. It is a single 

 gold-leaf suspended from the conducting-rod between 

 two dry piles, the negative pole of the one and the 

 positive of the other being uppermost. This showa 

 whether the electricity is positive or negative. 



For powerful electric storms, the self-registering ap- 

 paratus belonging to the atmospheric recorder is very 

 useful ; whilst a nicely-arranged electrical bell will be a 

 means of warning the observer that his presence is 

 required in the electric-room. 



The effect of a thunder-storm, when three or four 

 miles distant, as shown on these electrometers, is ex- 

 ceedingly interesting. It is not only possible to witness 

 the instantaneous convulsion caused by a flash of lightning, 

 at least twenty seconds before the peal of thunder occa- 

 sioned by it is heard, but it is also possible to know, 

 several seconds before a flash takes place, that one is 

 about to occur. 



The beneficial effects of electricity on the vegetable 

 kingdom are of a character so apparent, that any extended 

 researches upon the branch of Meteorology calculated 

 to throw additional light upon the subject is very 

 desirable. 



The Gimbal Vane. This is a wind-vane exactly 



