192 



SCIENCE 



[N. S. Vol. XLII. No. 1075 



down to the springing of the window arches 

 with a specially prepared felt. 



The felt as actually applied was two inches 

 thick on the ceiling, one inch thick on the side 

 walls. The work was carried out with admir- 

 able efficiency and carefulness. The appear- 

 ance of the chapel was practically unchanged, 

 so that no one, unaware of the treatment, would 

 have guessed that any application of the kind 

 had been made. 



Experiments extending over one college year 

 were made to test the effectiveness of the ar- 

 rangement. 



A college chapel service, where attendance 

 is required, affords a unique opportunity for 

 a study of this kind. Five regular services 

 weekly are held in the Adelbert College chapel. 

 One of these is a musical service; the other 

 four generally include a short address on some 

 practical or ethical subject. The services are 

 conducted by a number of clergymen from the 

 city, each of whom officiates in general all the 

 four days in a given week. It is possible, 

 therefore, for an observer to listen to the same 

 speaker for four successive days. The audi- 

 ence is practically the same each day, and the 

 general conditions are nearly constant, so that 

 the observations made on successive days are 

 comparable to a satisfactory degree. 



The experiments consisted simply in listen- 

 ing to a speaker on successive days, from 

 different parts of the auditorium, and noting 

 dovTn in each case the percentage of the words 

 spoken which were clearly understood. Effort 

 was made to consider only words which were 

 definitely heard, excluding as far as might be 

 those gained by association from the context. 

 Previous experiments, in connection with the 

 sounding-board, had given some facility in 

 this kind of work. Of course, only a rough ap- 

 proximation is possible, yet the margin of error 

 is perhaps less than would be at first supposed. 

 The attention is fixed, not on the number of 

 words understood, but on the number missed. 

 It is easy to distinguish approximately be- 

 tween the loss of one word in five, one in ten, 

 one in twenty; these correspond to an audibil- 

 ity of 80, 90 and 95 per cent., respectively. 

 95 per cent, means excellent hearing, 90 per 



cent, is fair, but if the number of words heard 

 is only 80 per cent, of the whole, the hearing is 

 positively poor, and below this runs rapidly 

 into unintelligibility. Perfectly satisfactory 

 hearing, clear and sharp, without effort or close 

 attention, is rated at 100 per cent. 



Four seats were chosen as places of observa- 

 tion, one in the front row of the gallery at the 

 back of the chapel, perhaps ninety-five feet 

 from the pulpit where the speaker stood, three 

 on the floor, seat AA, immediately under the 

 front edge of the gallery, about ninety feet 

 from the speaker, seats V and Q, respectively 

 seventy-five and fifty-five feet from the speaker. 

 The observer sat on successive days in each of 

 these seats in rotation, making notes as sug- 

 gested above. 



The chapel was treated with the absorbent 

 felt during the summer vacation of 1914. The 

 experiments began in February, 1914, while 

 the chapel was in its original condition, while 

 the second set, after the treatment of the 

 walls, extended from the latter part of Septem- 

 ber, 1914, to the end of February, 1915, the 

 whole including two college semesters. 



The relative number of words heard in the 

 case of each speaker having been evaluated as 

 closely as possible, the results were averaged 

 for each position of the hearer. For example, 

 in the seat AA, ninety feet from the speaker, 

 25 experiments were made during the first 

 semester, varying in intelligibility from 10 

 per cent, to 95 per cent. The average of all 

 the speakers was 71 per cent. This means that 

 on the average more than one word in four was 

 missed by the hearer. In almost every ease 

 the necessary attention was recorded as " care- 

 ful " or " strained." Listening was wearir 

 some, and it was often impossible to follow in- 

 telligently the purport of the address. 



In the second semester, sitting in the same 

 position, 28 speakers were heard. The average 

 audibility was 91 per cent. The attention 

 given was recorded as " easy " in about half 

 the cases, as " careful " in the others. In no 

 case was a tense or strained attention needful. 



The improvement in hearing was greatest, 

 of course, in the case of those who were heard 

 with difficulty, though in all cases the gain was 



