35 



BEAUFORT'S SCALE OF WIND FORCE, 



From the official iDstinctions of British Meteorologioal Office, with eimiTalent difference in level 

 I tube of Turpentine. 



Dili'erence of 



level Turpentine. 



inches. 



.010 



.068 



.184 



.!J5 



.58 



.87 

 I.2S 

 1.74 

 2.50 

 341 

 4.62 

 6.15 

 s 83 



The anemometer is r,mte inexpensive, perfectly simple in action, has a minimum of moving parts 

 and absolutely nothing to get out of order. It is so compact that all the mechanism is contained in a 

 small case and it records direction as well as pressure. In actual use it is best to fix the vane on the 

 top of a tall pole above the chimneys, etc. 



The instrument is complete with best French eight-day cloct and gives continuous records for 

 both pressure and dircctton. The instrument records every single puff of wind, and also tells when 

 -those puffs affected the instrument, and is thus much superior to the velocity instruments which 

 revolve at a great speed long after the puffs of wind have passed, and at best only give a very 

 approximate total velocity for a given total time. The instrument in use at Canterbury is fixed on 

 the roof on the top of 3.^ feet of one-inch galvanised iron tubing- it is 75 feet above the street b.-low 

 and records accurately through a pipe of less than J in. bore. 



A SIMPLE RECORDING GLYCERINE BAROMETER. 



This instrument consists of two bent glass tubes of about J-inch 

 bore fitted with stopcocks and connected together by means of stout 

 flexible "compo" tubing, as shown in the illustration. The head must 

 be about 3U feet above the bottom tube, but the flexible tube may 

 wind up a stair-case or any other way, so that the level of the 

 glycerine in the top glass tube is 27 feet above the level in the bottom 

 tube. On the glycerine in the open end of the lower tube is placed a 

 drop of ril to prevent the glycerine absorbing moisture from the 

 atmosphere, and in this floats an ordinary Erdmann float with a fine 

 spindle carrying a small pen which marks on an oidinary recording 

 drum. This drum is fitted with a setting screw which raises or 

 lowers the drum, and thus enables it to be set at any desired ma.-k 

 The hour mark is brought against the pen by setting the clock in 

 the usual way. The scale of the barometer inay be anything from about 

 11 inches for one inch of mercury downwards, this depending entirely 

 upon the ratio of the bore of two tubes. If the bore of each is half-inch 

 the scale would be about five inches for one inch of mercury. By means 

 of the filling tube the barometer can be filled with glycerine, and the 

 air driven out of the air trap in a few minutes without disturbing the 

 instrument This instrument is much more sensitive than a mercury 

 barometer, and sometimes indicates a change one hour or more before an 

 ordinary bar. .meter. The thunderstorm records are especially interest- 

 ing. The co-i fficient of expansion ..f glycerine works out to ■0C02S for 

 l" >■ ; this givfs a correction of OOS inch for every degree F. on a scale 

 e.|ual to 30 inches of mercury, but as the barometer is not confined in a 

 small room which is heated by fires, etc., it isnotliable to violent chang es 

 of temperature, and if set to a corrected standard instrument when .i new 

 chart is put on. it will only vary about 3' or 4° whilst the chart is ..n. 



