230 Royal Society .— 



Part I. 



At the last Meeting of the British Association I read a paper on 

 the precautions and corrections requisite in order that a more perfect 

 knowledge of ozone might he obtained. These precautions comprise 

 uniformity of observation, each observer using the same box and the 

 same tests, suspended at the same height, and as nearly as possible 

 placed under the same circumstances. The corrections necessary 

 are: — 1st, For the velocity of the air; 2nd, for the height of the 

 barometer ; 3rd, for temperature ; 4th, for the hygrometrical state 

 of the air ; 5th, for elevation above the ground. 



1. Velocity of the Air. — The greater the speed the more ozone 

 will be apparent, and this seems to be owing more to the increased 

 velocity of the air than to a greater proportion of ozone. 



2. Height of the Barometer. — It is found that during the last 

 four years, 



AVith the barometer at 28i inches the amount of ozone was 5'7 

 9 Q °. • ^ 



2 



2-0 



33 » <->\J 33 33 33 * 3 



J> }> OXJ-2 jj 33 33 U"4 



A law as regards ozone and pressure is clearly apparent ; but as the 

 barometer falls for wind, the excess at low pressures is no doubt 

 partly due to the increased velocity of the air. There is more ozone 

 with the wind between W.S.W. and S.S.E. than when between 

 N.N.W. and E.N.E., and the barometer is half an inch lower with 

 S.W. winds than with N.E. winds. 



3. Temperature. — Temperatures between 30° and 40° will give 

 less ozone than when between 40° and 50°, and the latter less than 

 when between 50° and 60°. The same holds good when the ozone 

 box is artificially warmed. This does not extend to very high tem- 

 peratures, because the great dryness of hot weather is against the 

 action of ozone on the tests. 



4. Moisture. — Increase of moisture up to a certain point is 

 favourable to the colouring of the tests, beyond w r hich it operates 

 unfavourably ; for when the air is completely saturated with moisture, 

 the effect of ozone is at its minimum. 



5. Altitude. — The higher the test is hung the darker will be the 

 colour obtained. The difference is as 4 to 6 between 4 feet and 

 35 feet above the ground. 



There are yet several other circumstances to be mentioned : — 

 1 . Hour of the Day. — The difference between the ozone readings 



at night and in the daytime are — 



In June and July an excess at night of 0*1 

 In August and September „ 0'4 



In October and November ,, 5 



In December and January ,, 0*8 



In February and March ,, 0'7 



In April and May „ 0v 



the average excess of the summer months being only one-half of 



that which occurs in winter. 



