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 condition and altitude it is quite possible to cause rain. The writer has seen it done, not once but many times; generally it must be admitted when the rain was not wanted. Maroons fired in wide-mouthed mortars have been used on the Continent for some years to break up hail clouds and bring them down in the form of rain over the vineyards, where a hail storm is a serious calamity to the wine grower.

The use of pyrotechnic signals in connection with aerial travel is gradually increasing. The stores used are practically those evolved and adopted during the great war, modified in some cases to suit peace time requirements, but substantially they are those described in the chapter on Military Pyrotechny.