io THE BOOK OF NATURE STUDY 



if the neighbourhood afford a hill which can be taken as a mimic 

 Mt. Blanc, a great deal of information could be driven home by a 

 teacher willing to take advantage of the child's joy in pretending. 



On a hill of a height suitable for an ordinary school excursion 

 the fall of temperature with increase of altitude is less easy to 

 demonstrate. The fall is roughly i F. for every 300 feet of rise of 

 altitude. If an attempt is made to show this, arrangements 

 should be made to have another thermometer read at the same 

 time at the bottom of the hill. If a direct observation of a fall of 

 temperature with a rise of altitude cannot be made, snow on the 

 summit of distant hills, or the snow lying on the uplands while it 

 has melted on the lower ground, can all be used to suggest the 

 fact of this fall of temperature. 



A mimic ascent of Mt. Blanc, then, whether conducted 

 wholly in imagination or by means of an actual ascent of a 

 local hill, has been taken as an opportunity to show that 

 both the barometer and the thermometer fall as we ascend. 

 As we stand on the top and look down on the valley below, 

 we note that if our hill is, say five hundred feet high, then five 

 hundred more feet of air weigh on the valley than upon us, and 

 we connect this fact with the slight fall in the aneroid. (The 

 barometer near sea-level falls rather more than one inch for 

 every thousand feet of rise.) We remember how de Saussure and 

 his companions gasped as they reached the top of Mt. Blanc, 

 and we realise that though the absence of five hundred feet of air 

 does not affect our breathing, yet when fifteen thousand feet of 

 air are absent matters are different. If the view from the hill- 

 top includes the sea it would be a suitable opportunity to suggest 

 that while we live at the bottom of an ocean of air, the fish in the 

 depths of the sea live at the bottom of two oceans, one of air and 

 another of water. 



We remember, also, that it is a little colder at the top of our 

 hill than on the plain, and that it is very much colder on the top 

 of Mt. Blanc than at Chamonix, so much colder that even in 

 summer the snow does not melt at the top. We take note, then, 

 that the air is thinner at the top of a hill than at the bottom, and 

 that at the same time it is colder, and we resolve to try and find 

 out if there is any relation between the two facts. 



