WEATHER BUREAU. 7 



One of the most serious drawbacks to grape culture in Europe is the 

 destruction caused by hail, and the growers are naturally interested 

 in anything that promises to give immunity from such damage. Dur- 

 ing the past two or three years renewed interest has been taken in 

 the matter by the vineyardists of certain parts of France and Italy. 

 Several manufacturers have placed upon the market a special form of 

 cannon which they claim will effectively break up hail-bearing clouds. 

 The belief in the efficacy of this method of protection lias become 

 quite general in Europe, although scientists versed in the physics of 

 the air have not expressed confidence in the system. 



In brief the apparatus in use consists of a cannon fitted with a fun- 

 nel-shaped conical extension. The difference between the various 

 forms of cannon that are used lies mainly in the shape and size of the 

 funnel extensions and the size of the powder charges. Usually the 

 cannon are fired vertically upward, although in some instances tiro 

 apparatus is inclined toward an advancing cloud. The effect of the 

 funnel attachment is to cause the formation of a mass of rapidly 

 revolving air, or vortex, which leaves the mouth of the cannon with 

 tremendous velocity. In shape, these vortices can be likened some- 

 what to the rings or puffs of smoke made by a person smoking a cigar. 

 It is claimed that these whirling masses of air, intermixed with gases 

 from the explosives, are forced upward to a sufficient height to enter 

 the hail cloud and destroy its hail-forming processes. If it is granted 

 that these rings ascend to a sufficient height to enter the cloud, I am 

 of the opinion that the force of the ring is too puny to have any appre- 

 ciable effect on the cloud. 



Many experiments have been made for the purpose of ascertaining 

 the actual height to which these air rings rise before being dissipated. 

 In a report by Profs. J. M. Pernter and W. Trabert, who, at the invi- 

 tation of the Imperial Department of Agriculture of Austria and of 

 the inventor of one of the methods, made as complete an investiga- 

 tion as was possible, and under various conditions, these scientists 

 stated that they were not able to report anything positi v^e as to the 

 value of hail shooting. They reported that, using the largest cannon 

 and the heaviest charges, the vortices did not ascend to a height of 

 1,000 feet on an average, although in some instances greater distances 

 were obtained. 



There is a marked difference of opinion as to the effectiveness of 

 cannon firing, with the manufacturers and many grape growers on the 

 one side and the scientists of America and Europe on the other. The 

 former maintain that hailstorms can be prevented in the manner 

 described, while the latter claim that the force exerted by the explo- 

 sives is infinitesimal as compared to the forces of nature that are 

 exerted in hail formation, and that experiments conducted by the 

 adherents of the cannonading process themselves have not produced 

 convincing results. The number of thunderstorms from which hail is 

 precipitated is but a small percentage of the actual number. In most 

 localities of the United States a whole season sometimes passes without 

 a fall of hail, while in seasons of abnormal thunderstorm frequency 

 the number of hailstorms is small. While in the grape-growing 

 regions of France and Italy there may be greater hailstorm frequency, 

 it is still true that the number of hailstorms are few as compared to 

 the number of thunderstorms without hail. The experimenters score 

 a success whenever they shoot at a thunderstorm cloud that does not 

 produce hail, although the chances are greatly in favor of there being 

 no hail in the cloud. Again, they excuse the occurrences of hail in 



