1875] WRITINGS OF JOSEPH HENRY. 453 



ourselves ready to admit the application of other principles, 

 or to modify our conception of those we have adopted when 

 new facts are discovered which warrant such changes. But 

 we require positive evidence, and cannot adopt any conclu- 

 sions which we think are not based upon a logical correla- 

 tion of facts. 



The investigations described in the following account — 

 though simple in their conception, have been difficult and 

 laborious in their execution. To be of the greatest practical 

 value they were required to be made on the ocean, under 

 the conditions in which the results are to be applied to the 

 use of the mariner, and therefore they could only be con- 

 ducted by means of steam-vessels of sufficient power to with- 

 stand the force of rough seas, and at times when these vessels 

 could be spared from other duty. The}'- also required a 

 number of intelligent assistants skilled in observation and 

 faithful in recording results. 



Observations in August, 1875, at Block Island. 



The party engaged in these investigations consisted of the 

 chairman of the Light-House Board ; General I. C. Wood- 

 ruff, U. S. A., engineer third light-house district; Dr. James 

 C. Welling, president of the Columbian University, Wash- 

 ington, D. C; Mr. T. Brown, of New York, patentee of the 

 siren; Mr. Edward Woodruff, assistant superintendent of 

 construction; and Captain Keeney, commander of the light- 

 house steamer Mistletoe. 



We arrived at Block Island on the afternoon of the 4th 

 of August, 1875. This place was chosen as the site of the 

 experiments, — first, on account of its insular position, being 

 as it were in the prolongation of the axis of Long Island 

 distant fifteen miles from the most easterly part of the latter, 

 and entirely exposed to the winds and waves of the Atlantic 

 Ocean ; and secondly, because there are on Block Island 

 two light-houses, one of which is of the first order, and con- 

 nected with it are two fog-signals, one of them with the latest 

 improvements. 



