Philadelphia and Erie R. R.; Pennsylvania R. R. Co., Lessee. Office of the General Superintendent, ERIE, PENN., May 19th, ’70. To GEO. M. MOWBRAY, North Adams, Mass., Dear Sir: The comparative values of the two materials, Gun-Powder and Nitro-Glycerin, as to results and actual cost for blasting in the harbor at Erie, cannot be positively obtained until the dredging is finished; when this year’s operations with Nitro-Glycerin, can be compared with that of last year done with powder. The prospects thus far are so favorable, however, I regret that the use of Nitro-Glycerin was not adopted last year. On the completion of the work I shall be pleased to furnish you with statements of comparative results, feeling confident they will prove a more full satisfactory and valuable endorsement of your Nitro-Glycerin for submarine use, than any theoretically based opinion can be. I enclose you copy of reports of Mr. F. J. Wilson, Engineer in charge of Erie Harbor Works, and of Mr. Dunbar, contractor for dredging, which will give you an idea of the economical results to us from the use of your Nitro-Glycerin. Yours truly, WM. A. BALDWIN, Gen’l. Supt. * * * * * ERIE, Penn., May 16th, 1870. WM. A. BALDWIN, Esq., Gen’l. Supt. P. and E. Railroad. Dear Sir: Below please find a statement of comparative cost of drilling and blasting where Nitro-Glycerin is used. The 1240 lbs. of Nitro-Glycerin were used over an area of 26,700 sq. feet, with an average depth of rock of about seven and seven-tenths feet, making 11,500 cub. yards of rock measured in the bed. Cost of drilling and blasting (using Nitro-Glycerin), $5,119 67. Cost of drilling and blasting (using Powder), 7,475 73. Difference of cost in favor of Nitro-Glycerin, 2,356 06. The difference in favor of Nitro-Glycerin in dredging and in time saved is not taken into consideration in the above (see Capt. Dunbar’s letter). Very respectfully, F. J. WILSON, Ass’t Engineer. * * * * * ERIE, May 18th, 1870. To W. A. BALDWIN, Esq., Gen’l. Supt. P. and E. Railroad,