104 ANNUAL RECOKD OF SCIENCE AND INDUSTRY. 



vessel remains vertical, the segment of the image of the hor- 

 izontal line will continue at a constant height upon the plate. 

 Consequently it would trace upon the plate a horizontal 

 line. Let us suppose now that the ship rolls ; at each in- 

 stant there would be a certain inclination, i, and at this mo- 

 ment a certain zone of the plate will be found behind the 

 opening of the shutter. The image of the horizon will traverse 

 this window at some point of this zone, and it will fall upon 

 the plate at a distance from the reference line equal to/", tang. 

 i. Experiments have been authorized according to this meth- 

 od, which is the invention of Huet, at Brest, and the photo- 

 graph proofs show the good results that were obtained. 



BAROMETRIC OBSERVATIONS ON THE OCEAN. 



Dr. Buys Ballot communicates in a preliminary way the 

 results of the great unpublished work undertaken by the Me- 

 teorological Institute of the Netherlands, and which consists 

 in the derivation from over three hundred thousand observa- 

 tions on board vessels of the average barometric pressure for 

 each month, and for every five degrees square throughout the 

 navigated portions of the North and South Atlantic Oceans. 

 The average barometric pressure within ten degrees of the 

 equator is 760.04 millimeters. The pressure within ten de- 

 grees of the parallel of 30 north is 765 millimeters; and 

 within ten degrees of the parallel of 30 south it is 762.5. 

 Beyond these latter parallels the pressure diminishes steadi- 

 ly toward the poles, and is, apparently, at the limits of Buys 

 Ballot's tables, viz., about 50 of latitude, in the southern 

 hemisphere, 750 millimeters, but in the northern hemisphere 

 760. Oesterreich. ZeitscJirift fur Meteorologie, X., 159. 



THE SMALL OSCILLATIONS OF THE BAROMETER. 



Hon. Ralph Abercrombie has examined the connection be- 

 tween the wind and the small oscillations of the barometer. 

 He finds, for example, that with an open window looking 

 south and the wind nearly south, in strong gusts the first 

 movement of the barometer is always upward, and about 

 one tenth of an inch, as if the effect of the wind on being re- 

 sisted by the house was to compress the air in the room. 

 In a corner house, one window open to the south and another 

 to the west, the Mind south, in strong gusts, with the west 



