VOL. XLIII.] PHILOSOPHICAL TRANSACTIONS. 37 



rate ; and a less one not permitting you to return the water out of the tube when 

 full, without the adhesion of a great deal to its sides ; which, when you have 

 placed the tube in its perpendicular situation, subsides, and sometimes fills up 

 ^ of an inch ; which, without care, must necessarily make great mistakes in 

 the diary. The method of graduating the board is this : 



He had a vessel of tin made, whose contents were exactly a cubic inch. With • 

 this vessel, filled with water exactly to its surface, he frequently gauged the tube, 

 till, by repeated trials, he had found the height to which a cubic inch of water 

 would rise in it. The space answering to this on the board he had graduated into 

 32 equal parts, and took the same method with the rest of the tube, till in the 

 same manner he had graduated 4 such inches. Now the surface of the funnel 

 being, as has been said, exactly a square inch, no rain can by it get into the 

 tube, but such as falls within the square of one inch ; which, as the shower is 

 more or less, has its exact quantity shown on the board, on which a moveable 

 index is placed. 



Of the Monihly Observations, — ^The vacant page at the end of every 4 weeks, 

 reserved for observations occurring in the preceding month, and giving a sum- 

 mary account of the greatest difference of the weather in it, is a method peculiar 

 to this diary ; and one which will be allowed exceedingly pertinent and usefiil. 

 The great end of this, and all diaries, is to furnish materials for a set of sound 

 observations, on which to build a thorough knowledge of the atmosphere, and 

 its effects on mankind : and it is easy to see what great advantage to this part 

 of natural knowledge must arise from a variety of observations, made by different 

 men of application and judgment, on one and the same subject. Besides, in 

 this portion of our design may be included, what could not well without per- 

 plexity be thrown into the columns of the diary, all the meteorological appear- 

 ances of the aurora borealis, lightning, thunder, &c. with abstracts of the most 

 authentic accounts of such phenomena, as at any time in the preceding month 

 have been seen in different parts of our own country, or abroad. 



A description of the meteorological figures in pi. 1. In fig. 12, aaaa shows 

 the hygrometer seen in the inside; bb the balance; c a small piece of wood, by 

 which the balance is fastened to the box; d the sponge; e the weight; f, f, two little 

 rings, by which the hygrometer is hung up. 



Fig. 13, the graduated plate on the front of the machine, with its index and 

 divisions. 



Fig. 14, the anemoscope; a the pedestal; b the pillar, in which the iron axis 

 is fitted; c the circle of wood, on which are described the 32 points of the com- 

 pass ; d the index ; e the wooden tube on its axis ; f the velum ; g the graduated 

 quadrant ; h the counterpoise of the vane. 



Fig. 15, the velum taken off; a the plane of the velum; b the spring; cc the 



