214 REPORT 1866. 



ot the same liquid. "WTieii limited volumes of water were employed, powerful 

 sounds were obtained in both cases ; but in large reservoirs we met with 

 an unexpected difRculty, for we found that musical sounds, which could be 

 heard through considerable distances in air, became totally extinguished at 

 very short distances from the point of origin in water. Even when sounds 

 were produced with considerable intensity in a confined vessel, as a pail or 

 tub, when the vessel was plunged in a large reservoir the sound communi- 

 cated to the air became remarkably deadened, and the intensity was more 

 diminished as the instrument was placed at a greater distance beneath the 

 surface of the water. The rapid extinction of musical sounds in water ren- 

 ders it almost hopeless to employ them for communicating signals in that 

 medium. 'SVe must therefore, if this investigation is to be continued, revert 

 to experiments similar to those of M. Colladon, and confine ourselves to the 

 transmission of shocks or impulses communicated to bars or pieces of metal 

 of various forms and dimensions. 



Report of the Lunar Committee for Mapping the Surface of the Moon. 

 By W. R. BiRT, at the request of the Committee, consisting of 

 James Glaisher, F.R.S., Lord Rosse, F.R.S., Sir John Herschel, 

 Bart., F.R.S., Professor Phillips, F.R.S., Warren De la Rue, 

 F.R.S., Rev. W. R. Dawes, F.R.S., Rev. T. W. Webb, F.R.A.S., 

 J. N. LocKYER, F.R.A.S., H. S. Ellis, F.R.A.S., Herr Schmidt, 

 and W. R. Birt, F.R.A.S. 



In the Eeport which I had the honour to present to the Members of the 

 British Association for the Advancement of Science at Birmingham, the 

 steps taken by the Committee appointed at Bath for ensiu'ing as full and 

 accurate a Register of Lunar Objects as could be obtained, wei'e described in 

 detail with the Forms issued by the Cominittee for obtaining this object, to 

 which were added a few notices of the more remarkable features of the Lunar 

 Siu'faee which had presented themselves in the course of observation. 



It was in the first instance proposed to construct an outline 5[ap of the 

 Moon's Surface foiu- times the area of that of Beer and Miidler, or 75 inches 

 in diameter ; every object entered in the Eegister to be inserted on the Map : 

 the outline of a Map of this size was exliibitedto the Section. 



In the Resolution reappointing the Committee, tlie object expressly men- 

 tioned, is that " of making further progress in mapping the surface of the 

 Moon ;" and while the Committee has not lost sight of the objects contem- 

 plated in its original appointment, it has, in consequence of some remarks 

 of the President of the Association, Professor Phillips, when the Report was 

 read, mainly directed its eflfbrts to the construction of an accurate outUne Map 

 of 100 inches in diameter. 



In noticing the progress made in this department of its labours, it may be 

 well to glance at the materials at present available for the purpose. These 

 are, well- determined positions of the First Order, and existing Photographs. 



In Appendix I. will be found the rectangular coordinates of all the posi- 

 tions of the fii'st order determined up to the time of Beer and Miidler. I am 

 not aware that any have been determined since, unless Herr Schmidt, of 

 Athens, may have added to the number, but his measures are as yet un- 

 publisned. 



