The sound made by a bombard's blast
How the wave of exploding powder strikes the air to produce the report.
A short note explains the origin of a bombard's report: the wave of blast thrown off by the ignited powder strikes against the resisting air, and that percussion of moving air upon still air is what makes the sound. The remark opens a run of pages on impact and percussion, and leads into the study of projectiles striking barriers taken up on the following folio.
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The blast-wave of the powder makes the sound
Leonardo traces a bombard's report to the wave of the blast thrown out by its ignited powder. As that wave drives against the opposing air, the percussion of the moving air upon the resisting air is what generates the sound.