72 THE LIFE OF SCIENCE 



planning; the plague of Milan in 1484 likely was his great oppor- 

 tunity in this field, and he thought of various schemes to improve 

 public sanitation and convenience, including a two-level system 

 of streets. Botany repeatedly fixed his attention and we find many 

 notes on the life of plants, the mathematical distribution of leaves 

 on a stem, also beautiful and characteristic drawings of various 

 species. A great deal of the work undertaken for his employers 

 was of course connected with military engineering: hundreds of 

 notes and sketches on all sorts of arms and armor, on all imagin- 

 able offensive and defensive appliances; of course, many plans for 

 fortifications and strongholds (how to attack them and how to 

 defend them); portable bridges; mining and countermining; 

 tanks; various devices for the use of liquid fire, or of poisoning 

 and asphyxiating fumes. He adds occasional notes on military and 

 naval operations. He had even thought of some kind of submarine 

 apparatus, by means of which ships could be sunk, but the 

 dastardliness of the idea had horrified and stopped him. 



No field, however, could offer a fuller scope to his prodigious 

 versatility and ingenuity than the one of practical mechanics. A 

 very intense industrial development had taken place in Tuscany 

 and Lombardy for centuries before Leonardo's birth; the pros- 

 perity of their workshops was greater than ever; there was a con- 

 tinuous demand for inventions of all kinds, and no environment 

 was more proper to enhance his mechanical genius. 



Leonardo was a born mechanic. He had a deep understanding 

 of the elementary parts of which any machine, however compli- 

 cated, is made up, and his keen sense of proportions stood him in 

 good stead when he started to build it. He devised machines for 

 almost every purpose which could be thought of in his day. I 

 quote a few examples at random : various types of lathes; machines 

 to shear cloth; automatic file-cutting machines; sprocket wheels 

 and chains for power transmission; machines to saw marble, to 

 raise water, to grind plane and concave mirrors, to dive under 

 water, to lift up, to heat, to light; paddle-wheels to move boats. 

 And mind you, Leonardo was never satisfied with the applications 



