The Equivalence of Energies
The leading scientists of the last two centuries have made clear that mechanical energies must remain conserved. That is to say, when energy is added to or taken away from an object, by changing its velocity or temperature, that energy must flow from or to another part of the system. This has been extensively tested and refined through a series of experiments.
The same is true for arcane energies: if an arcane effect is created, an equivalent amount of energy, whether arcane or mundane, must be expended. Conversely, if arcane energy is used, an equivalent effect must be produced.
Unfortunately, the nature of the formula for equivalence is not presently known. In particular, the conversion between arcane and mundane energies appears to be perplexingly complex.
Like a Moth to Flame
Fire has long been used in arcane rites. It represents a source of energy that can be focused to achieve arcane results or to open paths for the creatures of the occult. Even a single candle is a powerful tool in the hands of a skilled practitioner.The Explosive Problem
The increasing use of gunpowder has resulted in a thinning of the barriers between our world and the occult realms. Massive fusillades of muskets and cannons on the battlefield, where life is already being sacrificed, represents a serious risk of tearing open rifts that allow in occult entities.
Of course, virtually all of the powder used expends its energy hurling shot across the battlefield and producing thunderous blasts, but it is very likely that in the course of a battle, the "misfire" that instead is converted to arcane energy will go unnoticed.
The advent of more powerful explosives, such as nitroglycerin and Alfred Nobel's blasting powder, means that this problem is likely to get worse in the future.