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Some of the important details of the required shape and placement of parts learnt from this study are built into the cannon. Oddly other When ~e added in the idea apparently important that the explosive ~ave design features could be is essentially a pulse of done differently without ultrasonic sound and that any effect. What does such sound can cause which of c9~s~~_sgm2i~s_ -- wcaJ.lsea-aeIects-fn -- - - - - -our secre-t. solids and liquids in an effect called cavitation finally we had a reasonable theory about haw this thlOg might work. But that still seemed a fairly puny effect when it came to melting or smashing hailstones. So we then went back for a mare detailed look at how hailstones form and then we found they often are very fragile over a considerable time as they are forming. At this point we could make little further progress in thinking about it, and it came to doing it. E:Jtplosions Having seen a demonstration unit in operation, and noted its failure to operate reliably, particularly with an errat~c change in volume we proceeded to build our o~n unit. We designed a ne~ gas injection system ~hich provided an explosive charge shaped to SUIt the chamber, with the correct mixture of alr and gas. We also des1gned the horn to keep the exploSIve HAIL CANNON HANDBOOK sound focused in the a~ea above the cannon, and to shape the sound pulse so it would travel as far CIS needed. Meteorology Meteorology is the art or science of measuring and . predicting the weather. People have been trying to understand and predict the weather for All of recorded history, and some have become better at it than others. Despite the many books relating good solid facts about what happens when air and water move around in the atmosphere, actually predicting spec~fic weather at a specific time and place is best characterised as being least accurate when ~t is most important. When it comes to when and where a hailstGrm will occur, massive calculations on powerful computers usually prove only vaguely effectIve Oddly the reason for this MIKE EGGERS LTD. Nelson, New Zealand ..:;~~...)~-~:<._,,,,.,'i is no~ relatively well understood; it is that we cannot make accurate enough measurements of present conditions to provide the correct starting point for the calculations. Small changes in conditions some~here in the area covered by the calculations result in large changes in the final result, essentially because that is the nature of such __ --.CalCl.llations.... __ _ ___ - -- - - --- It is perhaps ironic that this is sometimes called a "snowball effect" in mathematlcs? InterestlnQlv it is the same effect which means the relatively small sound pulse from a hail cannon can change the outcome of a storm from hail to raIn in our theory. Fronts The big effects which cause ra~n and other sto~ms are called fronts. They are called warm or cold depending on the relative temperature of the fastest moving body of air. usually a cold front mov~ng In over warmer air sets up the conditions ~here parcels of lighter warm aIr push up through the heaVIer cold aIr. when this effect is suffiCIently VIgorous, Page 2