SEA-BREEZES, MOUNTAIN AIR, AND OZONE 255 



the local surface, whether it is heavy or rarefied, whether 

 it is dry or saturated with moisture. It is also an im- 

 portant fact that the atmosphere consists of layers and 

 currents differing in these qualities, and that the higher 

 layers can be reached by ascending to high-lying lands. 

 At the same time it seems that in a flat country the 

 ascent of a comparatively low hill brings you into a layer 

 or " stratum " of air differing more from that of the plain 

 or valley than would be the case were you to ascend to 

 the same height in a mountainous region. The seaside 

 and the mountain may owe the beneficial character of 

 their air to some of the varying qualities noted above. 

 Chemical differences may or may not be important, and 

 seem hardly to have been as yet brought within the range 

 of accurate knowledge. Ozone may be more or less 

 present, so may perfumes and volatile oils, such as are 

 given off by pine trees, and there may be more or less 

 minute quantities of carbonic acid and of sulphurous acid, 

 and still minuter quantities of the newly-discovered gases 

 argon and helium which, for all we know, may have 

 some effect on the human body. There seems to be a 

 great field open for accurate investigations in regard to 

 the action upon human health of all these varying con- 

 ditions of the air. In the meantime, we proceed by guess- 

 work, and are influenced by tradition and beliefs which 

 are based on a sort of experience, but are of a very vague 

 and unsatisfactory description. 



The case is much the same with regard to the natural 

 waters of celebrated resorts. So far as their chemical 

 composition is known, they can be manufactured and 

 applied for drinking or bathing anywhere. But minute 

 quantities of certain gases and other elements may be 

 present in these natural waters and have escaped until 

 now the observation of the chemist, and it is possible, 

 though not demonstrated, that these rare chemical con- 



