September 28, 1900.] 



SCIENCE. 



489 



and point, perhaps, to the original food-plant 

 of the San Jose scale. 



T. D. A. COCKEEELL. 



NOTES ON PHYSIOS. 

 ARCHITECTURAL ACOUSTICS. 



About five years ago Professor W. C. Sabine 

 was directed by the Corporation of Harvard 

 University to propose means for remedying the 

 acoustical defects of the lecture room of the 

 Fogg Art Museum at Cambridge. About two 

 years were spent in experimenting on this room 

 and permanent changes were then made. 



The experimental work done in connection 

 with this lecture room has led Professor Sabine 

 to take up seriously the general question of 

 architectural acoustics and we are promised a 

 series of papers on this subj ect the first of which, 

 on reverberation, is published in a recent num- 

 ber of the American Architect. 



In an introductory chapter Professor Sabine 

 gives a clear and comprehensive statement as 

 to the different ways in which sound is affected 

 by being confined in an audience room, substan- 

 tially as follows : 



The loudness of the sound is as a rule greater 

 at a given distance from the speaker than it is 

 in the open air. 



The character or timbre of a complex sound 

 is more or less altered by re-enforcement of cer- 

 tain of its elementary tones by resonance, or by 

 the re-enforcement or weakening of some of 

 its elementary tones at certain parts of the room 

 by interference. This alteration of the char- 

 acter or timbre of a complex sound Professor 

 Sabine calls ditortiosn. 



The sound persists in a room for a consider- 

 able time after the sounding body ceases to 

 vibrate. This is due to the more or less com- 

 plete reflection and re-reflection of the sound 

 from the walls, floor and ceiling. This persist- 

 ence of sound in a room Professor Sabine calls 

 reverberation. It causes the successive sounds 

 in articulate speech to overlap and become con- 

 fused. Especially the sonorous vowel sounds 

 persist, and obscure the delicate and fleeting 

 variety of the consonant sounds. 



The question of loudness becomes a serious 

 matter only in very large audience rooms. 



Sound distortion and reverberation depend 



very largely upon the same conditions. Thus 

 the extent to which an air column will enforce 

 the tone of a tuning fork depends largely upon 

 the length of time the air column will continue 

 to vibrate when left to itself after having been 

 set vibrating. Sound distortion is not so seri- 

 ous a matter as reverberation and, since the 

 two depend largely upon the same conditions, 

 it seems that reverberation only need be con- 

 sidered in any practical case. 



The reverberation of a room, measured by 

 the duration of a sound after the sounding 

 body ceases to vibrate, depends upon the ab- 

 sorbing power of the walls and of other reflect- 

 ing surfaces and upon the size of the room. 

 Thus heavily draped walls or walls lined with 

 thick felt absorb much and reflect little of the 

 sound which strikes them, and a sound persists 

 but a short time in a room of which a consider- 

 able portion of walls are padded or draped. 

 An audience also absorbs a large portion of a 

 sound in a room and greatly reduces reverbera- 

 tion. A larger room has greater reverberation 

 than a small room, walls being of similar ma- 

 terial, because the sound has farther to travel 

 between succeeding reflections, and a greater 

 time is therefore required for the absorption of 

 a given portion of the sound. 



Professor Sabine found that the note of a 

 particular organ pipe remained distinctly au- 

 dible in the lecture-room of the Fogg Art Mu- 

 seum for 5.6 seconds after the blowing of 

 the pipe ceased. The method proposed and 

 carried out for the reduction of reverberation 

 was to line a considerable portion of the walls 

 of the room with a thick hair felt. 



Professor Sabine has determined, by a very 

 ingenious method, the absorbing power of a 

 variety of wall surfaces, such as brick, plaster 

 on brick, plaster on lath, glass and boards, and 

 he has shown that the reverberation of a room 

 can be pre-determined by calculation in terms 

 of the size of the room and the character of 

 its walls. 



W. S. P. 



NOTES ON INORGANIC CSEMISTBY. 

 A VERY considerable amount of work is being 

 done at the present time in filling up the many 

 gaps that exist in descriptive inorganic ohem- 



