98 NATURAL THEOLOG f. 



our breath without reflecting what a work is thereby pei 

 formed, what an apparatus is laid in of instruments for the 

 service, and how many such contribute their assistance to 

 the effect. Breathhig with ease is a blessing of every mo- 

 ment, yet of all others it is that which w^e possess with the 

 least consciousness. A man in an asthma is the only man 

 who knows how to estimate it. 



IV. Mr. Home has observed,* that the most important 

 and the most delicate actions are performed in the body by 

 the smallest muscles ; and he mentions, as his examples, 

 the muscles which have been discovered in the iris of the 

 eye and the drum of the ear. The tenuity of these muscles 

 is astonisliing : they are microscopic hairs ; must be magni- 

 fied to be visible ; yet are they real, effective muscles, and 

 not only such, but the grandest and most precious of our 

 faculties, sight and hearing, depend upon their health and 

 action. 



V. The muscles act in the limbs with what is called a 

 mechanical disadvantage. The muscle at the shoulder, by 

 which the arm is raised, is fixed nearly in the same manner 

 as the load is fixed upon a steelyard, within a few decimals, 

 we will say, of an inch from the centre upon which the steel- 

 yard turns. In this situation, we find that a very heavy 

 draught is no more than sufficient to countervail the force of 

 a small lead plummet placed upon the long arm of the 

 stee^^yard, at the distance of perhaps fifteen or twenty inches 

 from the centre and on the other side of it. And this is the 

 disadvantage which is meant ; and an absolute disadvantage 

 no doubt it would be, if the object were to spare the force oi 

 muscular contraction. But observe how conducive is this 

 constitution to animal conveniency. Mechanism has always 

 in view one or other of these two purposes — either to mo\c 

 a great weight slowly, and through a small space, or to move 

 a li"ht weight rapidly through a considerable sweep. Fof 

 the former of these purposes a different species of lever, and 



* Philosophical Transactions, part I., 1800, p. 8. 



