8 



tridactylus, and in some measure also the didactylus, has a similar 

 distribution of these arteries. 



This peculiar disposition of the arteries in the limbs of these slow- 

 moving quadrupeds, it is thought cannot but retard the velocity of 

 the blood passing into the muscles of the limbs. Whence the well 

 known sluggishness of the animals, to whom this configuration seems 

 as yet peculiar, will perhaps be ultimately accounted for. Something 

 similar has been observed in the carotid artery of the lion, which 

 it is thpught may be subservient to the long continued exertion of the 

 muscles of his jaws, in holding a powerful animal for a length of time ; 

 and lastly, it is conjectured that the ruminating animals have a some- 

 what similar aplexus of arteries in the neck, which operates in retard- 

 ing the velocity of the fluids in those parts. 



Outlines of Experiments and Inquiries respecting Sound and Light. 

 By Thomas Young, M.D. F.R.S. In a Letter to Edward Whitaker 

 Gray, M.D. Sec.R.S. Read Jan. 1 6, 1 800. [Phil. Trans. 1 800, 

 p. 106.] 



We are here presented with a numerous set of experiments and 

 observations, which the author does not deliver as a series calculated 

 to elucidate any particular object, but rather as the results of the first 

 steps of an investigation ; which being of considerable magnitude, and 

 not to be accomplished in a short period of time, are here brought 

 forward in a detached form, in order to preserve them from oblivion, 

 should any unforeseen circumstances prevent his continuing the pur- 

 suit. They are classed under sixteen different heads, of which the 

 following are the titles, and some of the principal inductions. 



1 . Of the Quantity of Air discharged through an Aperture. This 

 was deduced from the quantity of pressure of water, on a body of air 

 rushing through a small aperture at the end of a tube. The result 

 was, that the quantity of air discharged by a given aperture is nearly 

 in the subduphcate ratio of the pressure ; and that the ratio of the 

 expenditures by different apertures, with the same pressure, lies be- 

 tween the ratio of their diameters, and that of their areas. 



2. Of the Direction and Velocity of a Stream of Air. These were 

 determined by the stream, produced by a known pressure, being made 

 to impinge, in a perpendicular direction, against a white plate, on 

 which a scale of equal parts was delineated, and which was thinly 

 covered with a coloured liquid. The results were here inferred from 

 the breadth of the surface of the plate laid bare by the stream. The 

 experiments being repeated at different distances between the orifice 

 and the plate, the longitudinal form of the stream could be hence de- 

 duced, their sections being bounded by curves, the nature of which 

 could be determined by their ordinates and abscissae. The nume- 

 rous results obtained in this manner are entered in various tables, 

 and likewise illustrated by figures, in which the longitudinal and not 

 the transverse sections are exhibited to the eye. 



3. Ocular Evidence of the Nature of Sound. This is produced by 



