284 Captain James on Meteorological Phenomena. 



the surface of the earth, we are not able to express numeri- 

 cally the effect of any increase or decrease in the tempera- 

 ture of the air upon the barometer ; but it has been shewn 

 by Colonel Sabine, that when the pressure due to the amount 

 of vapour in the air is deducted from the height of the baro- 

 meter, that the influence of temperature upon the dry air is 

 to produce a daily maximum and minimum, coinciding nearly 

 with the coldest and the warmest hours. 



2. Temperature of the air. — 



The maximum temperature registered on the 4th 



July, :.=r81°5 



The minimum temperature registered on the 19th 



February, , = 26°-0 



Extreme range during the year, =55°* 5 



The approximate mean temperature of the air for the year 

 = 48 0, 95, which is probably 2° or 3° higher than the mean 

 temperature of the air in the neighbourhood, in places beyond 

 the influence of the heat and shelter of the houses. 



3. Humidity. — The degree of humidity of the air has so 

 sensible an effect upon health, particularly on persons with 

 delicate lungs, or those subject to irritability of the skin, 

 that it is much to be wondered at that medical men in gene- 

 ral have paid so little attention to it, and more especially as 

 the instrument for measuring the humidity of the air in any 

 room is so simple and inexpensive. The gardener knows it 

 is not sufficient that his greenhouse should be kept at a cer- 

 tain temperature, but takes care that his plants shall have 

 also the requisite degree of moisture in the air ; without this 

 the plants droop ; and beyond doubt there is a certain degree of 

 moisture which is also necessary to the health of man. Every 

 sick room therefore should have a dry and wet bulb hygro- 

 meter ; and if the medical man considers that the tempera- 

 ture should be preserved at 60°, then the wet bulb thermo- 

 meter should indicate 55°, which would shew the air to be 

 •75, or three-fourths saturated with moisture. 



The amount of moisture might be regulated by exposing a 

 larger or smaller surface of water to evaporate, for which the 



