442 PHILOSOPHICAL TRANSACTIONS. [anNO 1788i 



which in part feeds itself, and is partly fed by the old ones till the approach of 

 the pairing season. If they did not go off in succession, it is probable we 

 should see them in large numbers by the middle of August ; for as they are to 

 be found in great plenty,* when in a nestling state, they must now appear very 

 numerous, since all of them must have quitted the nest before this time. But 

 this is not the case ; for they are not more numerous at any season than the 

 parent birds are in the months of May and June. 



The same instinctive impulse which directs the cuckoo to deposit her eggs in 

 the nests of other birds, directs her young one to throw out the eggs and young 

 of the owner of the nest. The scheme of nature would be incomplete with- 

 out it ; for it would be extremely difficult, if not impossible, for the little birds, 

 destined to find succour for the cuckoo, to find it also for their own young ones, 

 after a certain period ; nor would there be room for the whole to inhabit the 

 nest. 



XV. On the Temperament of those Musical Instruments, in which the Tones, 



Keys, or Frets, are fixed ; as in the Harpsichord, Organ, Guitar, ^c. By 



Mr, T. Cavallo, F. R. S. p. 238. 



The scale of music used at present consists of 7 principal notes or sounds, 

 which musicians denote by the letters of the alphabet a, b, c, d, e, p, g; which, 

 together with some intermediate ones, commonly called flats and sharps, and the 

 octave of the first, make 13 sounds. When those sounds are considered with 

 respect to the first, they are called by the following names, viz. the prime or 

 key-note, the 2d minor, 2d, 3d minor, 3d major, 4th, 4th major, 5th, 6th 

 minor, 6th major, 7th minor, 7th major, and octave. 



Musical sounds are produced by the vibrations of the sonorous bodies, and 

 they are acuter or graver as the vibrations performed in a given time are more or 

 less in number; so that if a string vibrating 100 times in a second produces a 

 certain sound, and another string vibrating 120 times in a second produces ano- 

 ther sound, the latter is said to be acuter, higher, or sharper than the former. 

 The number of vibrations performed in a certain time chiefly depends on the 

 thickness, length, and elasticity of the sonorous bodies ; but as the simplest 

 sonorous bodies, and the fittest for examination, are those strings which are 

 equal in every other respect, excepting in their lengths, because the number of 

 vibrations, which they perform in a given time, is inversely in the proportion of 

 their lengths, we shall consider only those in the present investigation, the 

 number of vibrations performed by other sorts of sonorous bodies being easily 

 deduced from them. As those 13 sounds are all different from each other, the 

 strings which produce them differ in length, and of course in the number of 



* I have known 4 young cuckoos in the nests of hedge-sparrows in a small paddock at the same 

 time.— Orig. 



