VOL. XIII.] PHILOSOPHICAL TRANSACTIONS. 5/9 



bestows on him an air-pump by his side, by which he may make himself hea- 

 vier or lighter, in imitation of the engines nature has given to fish for that use. 

 By this means he avoids the objections the others are liable to, particularly that 

 of the air, the moisture with which it is clogged in expiration, and by it 

 made unfit for the same use again, being here taken from it by its circulation 

 through the pipes, to the sides of which it adheres, and leaves the air as un- 

 tainted as before. 



He concludes this first part with a description of the diving ship, the motion 

 of which he conceives would be much facilitated by one single oar in the poop, 

 which should be flexible, and made with a spring, from the vibration of which 

 the ship should be impelled as fishes are by their tails. 



In the second part the author describes the mechanical mode, and assigns the 

 immediate cause, by which the contraction of the muscles is performed. 



Concluding that the muscles are contracted from the inflation of their fibres 

 by adventitious bodies, as it were by wedges ; and having refused an incorpo- 

 real natural faculty for the immediate mover, as also any aerial substance, and 

 rejected the blood filling the pores of the muscles, together with the manner 

 by which moistened ropes are contracted, he infers, that the ebullition, caused 

 in the muscles by the concurrence of the blood and succus nerveus, is the im- 

 mediate cause of the intumescence and contraction, which he confirms and il- 

 lustrates by arguments and experiments. 



He next gives an account of the internal motions of the fluids of the body, 

 as of the circulation of the blood. Describing the muscular structure of the 

 heart, and showing how it differs from other muscles by the wonderful texture 

 of its fibres. 



He at last infers that the moving faculty of the heart exceeds the resistance 

 of the whole blood in the arteries, and of the ligaments that hinder their dila- 

 tation, which is greater than the force of a weight of 180,000. 



He ascribes respiration wholly to the muscles that enlarge the thorax, viz. 

 the intercostals and the diaphragm, together with the weight and elasticity of 

 the air. The manner, by drawing up the circumference of the ribs towards the 

 throat, by directions that make acute angles with the planes of the ribs. The 

 structure of the thorax in the tortoise, he observes, is remarkable, there being 

 no divided ribs, but one continued bony arch, and no diaphragm ; and instead 

 of lungs, 2 long bladders, containing also the blood-vessels. These bags are 

 not alternately filled and emptied, but constantly remain full of air, which is 

 not renewed in them but partially, by the external muscles that stick to the 

 skin, which when inactive make a hollow sinys, but contracted a plane. 



Then follow some observations on the nutrition of plants, on the use of the 



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