44 REPoiiT — 1873. 



On Experiments on Euaporation and Temperature made at WisbeacJi. 

 By S. B. J. Skertchly. 



On the Passage of Squalls across the British Isles. 

 By G. M. Whipple, B.Sc, F.R.A.S., of the Keiv Observatory. 



After exhibiting the uncertainty attendant upon investigation of meteorological 

 laws by the aid of observations made over a small part of the earth's surface like 

 the British Isles, owing to tlie want of well-marked characteristics which would 

 serve to identify and track out masses of air moving over the couutiy, the author 

 calls attention to squalls which, occurring abruptly and presenting certain definite 

 features, are recorded in a conspicuous manner by self-registering meteorological 

 instruments when they pass over them. 



The appearance of the instrumental curves at the time of a squall was described 

 and illustrated by means of tracings from the Quarterly Weather Reports of the 

 Meteorological Committee ; and a table was given showing a brief history of twenty- 

 three squalls, registered in the Reports from 18G9-73. 



From this it appeared that their motion is almost invariably in a direction from 

 westward to eastward, with a velocity diminishing as they progress. 



The velocity of the easterly motion is sometimes as high as 100 miles per hour, 

 and falls as low as 10 miles, the average rate given by the whole series being 38 

 miles per hour. 



Refen-ing to other papers which have appeared on these phenomena, the author 

 suggests that use might with advantage be made of a better knowledge of squalls 

 in issuing storm warnings. 



Insteuments. 



On Dynamometers in Absolute Measure. 

 By Robert Stawell Ball, LL.D., F.E.S. 



On an Improvement in the Sextant. By Capt. J. E. Davis, B.N., F.E.G.S. 



This small adaptation to the sextant is intended principally to facilitate the taking 

 observations of heavenly bodies, of course with the view of fixing positions, rating 

 chronometers, &c. It consists of two parts, viz. the micrometer and the indicator. 

 The micrometer is simply a toothed wheel attached to the tangent-screw ; and to 

 the arm of the sextant is attached a pawl or click, adapted to the toothed wheel. 

 Each tooth represents one tenth of the circumference or turn of the tangent-screw ; 

 so that (presuming the tangent-screw to be correct) whatever alteration one turn 

 of the screw makes in the reading on the arc, each click represents exactly one 

 tenth of that movement ; thus, if one turn of the screw moves the vernier 20 

 minutes, each click moves it exactly 2. 



The indicators are two movable brass slides, one placed before the arm, the 

 other behind the arm of the sextant, and capable of being clamped firmly. By 

 means of these there is no necessity to read off the observations at the time of 

 observing. 



The micrometer movement can be disconnected at pleasure by means of a small 

 eccentric, which lifts the pawl. 



In using the sextant, if the heavenly body is rising, the indicator behind the arm 

 is moved with the arm in bringing the reflected image down ; and before it comes 

 into contact either with the horizon or its own reflection in the artificial horizon, the 

 arm is clamped, and the indicator also. The first contact is the first observation. The 

 tangent-screw is then quickly turned one or two clicks ; this opens or separates the 

 two images, which; on coming into contact again, form the second observation ; and 

 so on. 



