an army to proceed on its plan of advance, and, on the other hand, the ice may help a pursuing army to follow its retreating enemy without the delay needed for building bridges. In 1780, troops were led on the ice from New Jersey to Staten Island, to attack the British, and provisions were sent across on sleighs. In 1809, the Russians were led to Sweden across the frozen Gulf of Bothnia. Sudden thaws after severe cold are often serious handicaps in a campaign. Roads and fields are suddenly turned from hard ground into deep mud or swamp, and the movement of troops, and especially of guns and supplies, may be stopped. Heat has caused as great suffering as has the cold, but less often, in our latitudes. The sufferings of the French army under General Kléber in Egypt in 1798 are well known to students of history. Officers threw themselves on the sand and gave way to despair.
If we look over the foregoing, and many other cases of weather controls in war, it is easy to see that these examples may be grouped in two classes. In one of these, the particular weather condition or phenomenon was so to speak accidental; it was sudden; unexpected at that special time; and therefore hardly to be guarded against. Cases of this sort are the sudden storms which have so often been decisive factors in military undertakings. In the second class the weather conditions were perfectly normal and natural for the particular region and season in which they occurred, but the army was not prepared for them because of the ignorance, or lack of foresight, or over-confidence, or haste, on the part of the commanding officers. Thus, the terrible disaster which befell the French army in Russia was largely due to Napoleon's own recklessness in rushing unprepared troops into the teeth of a northern winter. Cold and snow contributed towards making a disaster complete which would probably have been a serious one under any meteorological conditions. Again, during the British expedition into Tibet, a few years ago, great difficulty was experienced at the higher altitudes owing to the hardening of the oil in the guns, on account of the cold, and the low boiling point at those great altitudes made it difficult to cook food properly in the absence of special cooking utensils adapted for use at low pressures. These handicaps could have been provided against if proper care had been taken beforehand.
It is clear that weather, although not always, or ultimately, is a factor which must be reckoned with in warfare. It is one of a large number of factors, among which topography, soil, hydrography, vegetation, and so on, must also be included. To know, in advance, the general climate of the war zone; to be prepared for the special weather conditions which are reasonably to be expected at this or that season; to have as accurate a knowledge as possible of the probability of occurrence of severe cold; of sudden thaws; of heavy rains; of great heat; of high winds; of deep snows—this is a very essential element in plan-
