i The Right Eon. Lord Bayleigh [Jan. 17, 



guarderl, but a more equable distribution of the sound from a single 

 horn remains a desideratum. 



Guided by the considerations already explained, I ventured to 

 recommend to the Trinity House the construction of boms of novel 

 design, in whicb an attempt should be made to spread the sound out 

 horizontally over the sea, and to prevent so much of it from being 

 lost in an upward diiection. The solution of the problem is found 

 in a departure from the usual circular section, and the substitution 

 of an ellij^tical or elongated section, of which tbe short diameter, 

 placed horizontally, does not exceed the half wave-lengih ; while the 

 long diameter, placed vei tic illy, may amount to two wave-lengths or 

 more. Obliquity in the horizontal plane does not now entail much 

 diiference of phase, but when the horizontal plane is departed from 

 such differences enter rapidly. 



Horns upon this principle were constructed under the supervision 

 of Mr. Matthews, and were tried in the course of the recent experi- 

 ments off St. Catherine's. The results were considered promising, 

 but want of time and the numerous obstacles which beset large-scale 

 operations prevented an exhaustive examination. 



On a laboratory scale there is no difficulty in illustrating the 

 action of the elliptical horns. They may be made of thin sheet 

 brass. In one case the total length is 20 cm., while the dimensions 

 of tlie mouth are 5 cm. for the long diameter and 1\ cm. for the 

 shorter diameter. The horn is fitted at its narrow end to A (Fig. 1), 

 and can rotate about the common horizontal axis. When this axis 

 is pointed directly at the flame, flaring ensues ; and the rotation of 

 the horn has no visible effect. If now, while the long diameter of 

 the section remains vertical, the axis be slewed round in the hori- 

 zontal plane until the obliquity reaches 60° or 60°, there is no im- 

 portant falling off in the response of tbe flame. But if at obliquities 

 exceeding 20° or 30° the horn is rotated through a right angle, so as 

 to bring tbe long diameter horizontal, the flame recovers as if the 

 horn had ceased sounding. The fact that there is really no falling 

 off may be verified with the aid of a reflector, by which the sound 

 proceeding at first in the direction of the axis may be sent towards 

 the flame. 



When the obliquity is 60° or 70° it is of great interest to observe 

 how moderate a departure from the vertical adjustment of the longer 

 diameter causes a cessation of effect. The influence of maladjust- 

 ment is shown even more strikingly in the case of a larger horn. 

 According to theory and observation a serious falling ofl' commences 

 when tbe tilt is such that the difference of distances from tbe flame 

 of tlie two extremities of the long diameter reaches the half wave 

 length — in this case 1 cm. It is thus abundantly proved that the 

 sound issuing from the properly adjusted elliptical cone is confined to 

 a comparatively narrow belt round the horizontal plane and that in 

 this }.lune it covers efficiently an arc of 150° or 160°. 



Another experiment, very easily executed with tbe apparatus 



