SMOKE AND DUST ABATEMENT COTTRELL. 685 



Sir Oliver Lodge and his sons are also once more active in this 

 field and are likewise joining very cordially in the general spirit of 

 cooperation. Their recent technical contributions to the subject^ 

 have been chiefly in the lines of rectification and insulation. Figure 

 57 shows some of this high potential current rectifying apparatus, 

 the most novel and essential element of which is a special form of 

 \'acuum tube which permits the current to flow' through it only in 

 one direction. This may be used either by itself or preferably in 

 conjunction Avith a mechanical rectifier such as those already de- 

 scribed. It appears to have been first devised and used for experi- 

 ments on the stimulation of gi'owing crops by high potential unidi- 

 rectional discharges," but its applicability and importance in precipi- 

 tation work is now being thoroughly investigated, and positive data 

 on this from large-scale tests should soon be available. It is only 

 within the last year that a really active commercial development of 

 the electric precijiitation processes has been undertaken in Eurox3e, 

 but at the present time several installations are under constnictiou 

 in various countries, and it is hoped that later a detailed report of 

 this work may also be possible. 



1 British Patents 25047 and 25047a (1905), also 29268 and 29269 (1912). 

 8 John Ernest Newman and Lionel Lodge, Brit. Pat. 17046 (1907). 



