390 THE FARMER AT HOME. 



is no instance of any bird singing whose size exceeds that of our black- 

 bird ; and this is supposed to arise from the difficulty it would have 

 of concealing itself, did it call the attention of its enemies, not only by 

 its bulk, but by the proportionable loudness of its notes. 



It has been noticed by some writers, that certain passages of the 

 song in a few kinds of birds correspond with the intervals of our scale, 

 of which, indeed, the cuckoo affords a striking and well known 

 instance ; but much the greater part of such song is not capable of 

 musical notation ; partly because the rapidity is often so great, and it 

 is also so uncertain when they may stop, that we cannot reduce the 

 passages to the form of any musical bar whatsoever ; partly also, 

 because the pitch of most birds is considerably higher than that of the 

 shrillest notes of our highest instruments ; and principally because the 

 intervals used by birds are commonly so minute and consequently so 

 different from the more gross intervals into which we divide our 

 octave, that we cannot judge of them. 



Most people, who have not attended to the notes of birds, suppose 

 that all those of the same species sing exactly the same notes and 

 passages, which is by no means true, though it must be admitted that 

 there is a general resemblance. The nightingale has been almost 

 universally esteemed the most capital of singing^ birds ; and its 

 superiority chiefly consists in the following particulars ; its tone is 

 much more mellow than that of any other bird, though by the exer- 

 tions of its powers it can be extremely brilliant. Another point of 

 superiority is its continuance of song without a pause, which is often 

 extended to twenty seconds. 



SPECTRUM. In Optics, when a ray of light is admitted through 

 a small hole, and received on a white surface, it forms a luminous 

 spot. If a dense transparent body be interposed, the light will be 

 refracted in proportion to the density of the medium ; but if a triangu- 

 lar glass prism be interposed, the light is not merely refracted, but 

 divided into seven different rays. The ray of light no longer forms a 

 luminous spot, but has assumed an oblong shape, terminating in semi- 

 circular arches, and exhibiting seven different colors. This image is 

 called the spectrum, and, from being produced by the prism, the pris- 

 matic spectrum. These different colored rays appearing in different 

 places of the spectrum, show that their refractive power is different. 

 Those which are nearest the middle are the least refracted, and those 

 which are the most distant, the greatest. 



The order of the seven rays of the spectrum is the following ; red, 

 orange, yellow, green, blue, indigo, violet. The red, which is at one 

 end of the spectrum, is the least, and the violet, which is at the other 

 end, is the most refracted. Sir Isaac Newton found, if the whole 

 spectrum was divided into 360 parts, the number of the parts occupied 

 by each of the colors tc be the following ; red, 45 parts ; orange, 27 ; 

 yellow, 48 ; green, 60 ; blue, 60 ; indigo, 40 ; and violet, 80. Theso 



