designed to accommodate Spectators and Auditors. 133 



comfort, in an easy posture, and as clearly as if no other indi- 

 vidual auditor or spectator were present. (See Plates I. and II.) 



The position of the seats is the first circumstance we shall in- 

 vestigate. Thats eats should slope, or, in other words, that the 

 more distant auditors should be raised above those who are 

 nearer, is at once seen ; the question is how, and how much .^ 



To see and hear comfortably, it must not be necessary for us to 

 remain long in one position ; we must not require to sit upright 

 at full stretch, or to stoop on one side to catch a glance between 

 an avenue of heads or hats ; we must be permitted, whether tall 

 or short, to sit in a comfortable variety of attitudes, now a little 

 back on the seat, then a little forward, now stooping down, and 

 now raised upright. In the usual variety of station and of po- 

 sition, it appears from experiments we have made that the range 

 required for this purpose is more than a foot and less than 18 

 inches, so that these may be taken as the limits ; that is to say, 

 over the head of the person who is before you, there must be a 

 clear range of 12 or 18 inches, through which the head may be 

 moved upwards or downwards without interruption. In other 

 words, as the undulations, both .soniferous and luminiferous, move 

 in straight lines, it is necessary for the purpose, that the rays 

 of light and of sound emanating from the speaker, may fall, 

 without interruption, on the organs of sight and hearing of the 

 spectators and auditors ; that a straight line drawn from the 

 speaker's head over that of the anterior .spectator, shall inter- 

 cept the straight line wliich forms the back of the seat of the 

 posterior observer, so as to cut off a height of 12 to 18 inches, 

 within which the head of the spectator shall at all times be com- 

 prehended while sitting in a comfortable position. Thus let A 



Fiff 1. 



be the speaker, and X YZ be three successive ascents ; then 



