316 THE CHEMICAL HISTORY OF AIR. 



were no dust in the air,' said Aitkin, ' there would be no fogs, no 

 clouds, no mists, and no rain.' Our obligations to this discoverer 

 were completed by his invention of the ' Koniscope,' a small and 

 portable instrument for testing rapidly and easily the air in our 

 cities and rooms — an instrument which every sanitary inspector 

 would find of use. It was not to determine the absolute number 

 of dust particles in the air that the Koniscope was chiefly used, 

 but to compel them to tell by their behaviour and colour in a ray 

 of light whether the dust particles present were few or many. 



Mr. Aitkin thus describes his method of making impure air 

 visible : — 'The room is tested in every part, and the inside air 

 gives, like the air outside, only the faintest colour. Three jets of 

 gas are then lit in the centre of the room, which has the dimen- 

 sions of 24 ft. by 17 ft. by 13 ft. Within thirty-five seconds of 

 striking the match to light the gas, the products of combustion 

 had extended to the end of the room, for the colours in the Koni- 

 scope had become dark blue ; in four minutes the deep blue- 

 producing air was found at a distance of two feet from the ceiling, 

 and in ten minutes there was evidence of the pollution all through 

 the room. It was strongly indicated near the windows, owing to 

 the downward currents of cold air on the glass, and the impure 

 currents could be traced to the floor and onwards to the fireplace, 

 while a pure current could be traced from the door to the fire- 

 place.' 



It had been proved, however, that great epidemics like the 

 cholera were not spread in their ordinary course by the air, for 

 they did not travel faster than human intercourse, and it was for- 

 tunate for us that such was the case, but in certain circumstances 

 — in the neighbourhood of infected spots, for instance — the air 

 was known to be a medium of infection for short distances. If 

 this half century had so extended our knowledge of nature, what 

 may we not expect in the coming century ? " — Mon, Mag. Phar. 



For utilising the services particularly of mammals, many fruits 

 have developed hooks or horns to catch in the fleece of passing 

 creatures, who thus transport the seeds from place to place. An 

 autumn tramp through our pastures will soon convince one of the 

 efficiency of this mode of dissemination. 



