552 THE POPULAR SCIENCE MONTHLY. 



our return to Dover Bay, at 10 p.m., we heard the sounds, not only 

 distinct but loud, where nothing could be heard in the morning. 



Remarkable Instances of Acoustic Opacity. In his excellent 

 lectm-e entitled " Wirkungen aus der Feme," Dove has collected some 

 striking cases of the interception of sound. The Duke of Argyll has 

 also favored me with some highly-interesting illustrations. But nothing 

 of this description that I have read equals in point of interest the fol- 

 lowing account of the battle of Gain's Farm, for which I am indebted 

 to the Rector of the University of Virginia : 



"Lynchburg, Va., March 19, 1874. 



" Sie : I have just read with great interest your lecture of January 16th, on 

 the acoustic transparency and opacity of the atmosphere. The remarkable ob- 

 servations you mention induce me to state to you a fact which I have occa- 

 sionally mentioned, but always, where I am not well known, with the apprehen- 

 sion that my veracity would be questioned. It made a strong impression on me 

 at the time, but was an insoluble mystery until your discourse gave me a pos- 

 sible solution. 



" On the afternoon of June 28, 1862, 1 rode, in company with General G. W. 

 Randolph, then Secretary of War of the Confederate States, to Price's house, 

 about nine miles from Richmond ; the evening before General Lee had begun 

 his attack on McClellan's army, by crossing the Chickahominy about four miles 

 above Price's, and driving in McClellan's right wing. The battle of Gain's Farm 

 was fought the afternoon to which I refer. The valley of the Chickahominy is 

 about one and a half mile wide from hill-top to hill-top. Price's is on one hill- 

 top, that nearest to Richmond ; Gain's Parm, just opposite, is on the other, 

 reaching back in a plateau to Cold Harbor. 



" Looking across the valley I saw a good deal of the battle, Lee's right rest- 

 ing in the valley, the Federal left wing the same. My line of vision was nearly 

 in the line of the lines of battte. I saw the advance of the Confederates, their 

 repulse two or three times, and in the gray of the evening the final retreat of 

 the Federal forces. 



" I distinctly saw the musket-fire of both lines, the smoke, the individual dis- 

 charges, the flash of the guns. I saw batteries of artillery on both sides come 

 into action and fire rapidly. Several field-batteries on each side were plainly in 

 sight. Many more were hid by the timber which bounded the range of vision. 



" Yet, looking for nearly two hours, from about 5 to 7 p. m. on a midsummer 

 afternoon, at a battle in which at least 50,000 men were actually engaged, and 

 doubtless at least 100 pieces of field-artillery, through an atmosphere optically 

 as limpid as possible, not a single sound of the battle was audible to General Ran- 

 dolph and myself. I remarked it to him at the time as astonishing. 



" Between me and the battle was the deep, broad valley of the Chickahom- 

 iny, partly a swamp, shaded by the declining sun, by the hills and forest in the 

 west (my side). Part of the valley on each side of the swamp was cleared; 

 some in cultivation, some not. Here were conditions capable of providing sev- 

 eral belts of air, varying in the amount of watery vapor (and probably in tem- 

 perature), arranged like lamina? at right angles to the acoustic waves as they 

 came from the battle-field to me. 



" Respectfully, your obedient servant, R. G. H. Kean. 



" Prof. John Ttndall." 



