1875] 



WRITINGS OF JOSEPH HENRY. 



481 



though of higher velocity than on any other occasion, was 

 variable. On this day the experiments were principally 

 made with the Mistletoe. The Cadvs (being obliged to leave 

 on other duty) ran one course a distance of two-thirds of a 

 mile before the sound of her whistle was lost at the light- 

 house. She afterwards steamed off in the direction c b (Fig. 

 10), noting the sound of the siren, which was lost at the 

 point 6, afterward regained, and heard distinctly ten and 

 one-half miles distant. 



During the passage of the first course of the Mistletoe, the 

 wind at the surface and above was from south-west, the latter 

 being indicated by a cloud passing the zenith. During the 

 .second course the wind was variable, changing its direction 

 about 90°, principally from the north-west; while during the 

 third course the wind was again from the south-west. The 

 long course of the Cactus marked on the figure indicates the 

 sound of the siren from the centre outward, as it was heard 

 seven and one-fourth miles, then lost for an interval, and 

 afterward heard again at a distance of three and one-fourth 

 miles farther, making in all ten and one-half miles. 



Experiments of September 7. — Barometer, 301 inches; ther- 



