Whilst directing the military affairs of the Duke of Bavaria he had to organise the field artillery, and he found no cannon foundry in Bavaria. The arsenal at Munich was filled with cannon, but by far the greater part of them were perfectly useless, being too heavy to be moved. There was a very good foundry at Mannheim, the capital of the Elector’s dominions on the Rhine, but the distance between Munich and Mannheim is so great that it would have cost more to have sent the Bavarian guns to Mannheim to be refounded and to have brought them back than was required to defray the expense of establishing a new manufactory for the construction of artillery in Bavaria.
A foundry was accordingly established at Munich, and neither pains nor expense were spared to make it as perfect as possible. A most excellent machine was erected for boring cannon, with workshops adjoining to it for the construction of gun-carriages and ammunition waggons.
Whilst engaged in superintending the boring of the cannon he was struck by the heat produced in a brass gun and with the still more intense heat of the metallic chips separated by the borer.
He says: ‘The more I meditated on these phenomena the more they appeared to me to be curious and interesting. A thorough investigation of them seemed even to bid fair to give a further insight into the hidden nature of heat, and to enable us to form some reasonable conjectures respecting the existence or non-existence of an igneous fluid.
‘Whence comes the heat actually produced?
‘Does it come from the metallic chips? If so, their capacity for heat must be changed; but by repeated experiments I found that no change of capacity was caused by the boring. Determination of the actual heat produced and of the amount of chips showed that there was no relation between them. That the heat did not come from the gun itself was shown by the absence of every sign of exhaustion in the metal, notwithstanding the large quantities of heat given off.
‘Did the heat come from the air? Exclusion of the air did not in the smallest degree diminish the heat.
‘It would be difficult,’ he says, ‘to describe the surprise and astonishment expressed in the countenances of the bystanders on seeing a large quantity of cold water heated and actually made to boil without any fire.
‘Though there was, in fact, nothing that could justly be considered as surprising in this event, yet I acknowledge fairly that it afforded me a degree of childish pleasure which, were I ambitious of the reputation of a grave philosopher, I ought most certainly rather to hide than to discover.’
The amount of heat given out in a continual stream by his borer he estimated at that of nine wax candles each of three-quarters of an inch in diameter. This was produced by the work of two horses. ‘But,’ he adds, ‘no circumstances can be imagined in which this method of procuring heat would not be disadvantageous; for more heat may be obtained by using the fodder necessary for the support of a horse as fuel.’