METEOROLOGY. 531 



tables give the true direction and velocity of cloud movement with equal 

 ease. (Z. 0. G. M., xvm, pp. 90-92.) 



Prof. O. Jesse describes three methods of determining the altitude 

 of the clouds, as follows : First, a beam of brilliant light is thrown upon 

 some spot on a cloud which being thus illuminated is observed as to 



r altitude and azimuth from two stations, and a trigonometric calculation 

 gives the altitude. Second, an observer is furnished with a simple plane 

 table divided into small squares of l mm each; at an observed moment 

 the-location of the cloud is observed on this plate; the same is doue a 

 second time without change of instrument, whence results the apparent 

 movement of the cloud. Let the observer now change his location by 

 a known distance perpendicular to the direction of movement of the 

 cloud and make a third and fourth observation of the cloud's location 

 on his plane table and he has at once all the material necessary for de- 

 termining height and motion of the cloud. Third method: this is sim- 

 ilar to the preceding, except that a camera- obscura replaces the plane 

 table. [It may be worth while to note that in 1872 and 1874 the writer 

 presented for the consideration of General Myer a sketch of numerous 

 methods for determining the altitude and motions of clouds, some of 

 which at that time had already been published, while others seemed 

 new. Among these latter were the following : First, by means of two 

 cameras mounted on alt-azimuth circles, successive photographs of 

 clouds are to be taken, whence their altitudes and internal changes 

 could be determined. Second, by a vertical beam of light and the 

 observation of the illuminated spot overhead calculate the height of the 

 lower surface of clouds at night. Third, by a mirror movable about 

 horizontal and vertical axes observe the apparent altitude and van- 

 ishing point of the horizontal movement of a cloud in any portion of 

 the sky. Fourth, by two small houses a few hundred feet apart, fitted 

 up as camera-obscuras, with lenses overhead and horizontal tables 

 below, record on sheets of graduated paper the locations at successive 

 moments of the image of clouds, whence altitudes and motions can be 

 calculated. While this note can at present have but slight historical 

 interest, yet the subject continues to be one of growing importance, 

 and will, it is hoped, commend itself to the attention of the reader.J 

 (Z. 0. G. M., xxxi, p. 181.) 



Dr. W. W. Linss publishes an essay on the origin of streaky forms of 

 cirri ordinarily known as "mare's tails," polar bands, and other varie- 

 ties. The principal stria} are either homogeneous massesor they show the 

 beautiful incipient formation known as mackerel sky. The axes of the 

 principal striae are almost always straight lines, and ofteu of great length ; 

 the secondary striae are either perpendicular or parallel to the original, 

 forming a system of equidistant wave-marks. Linss maintains that the 

 formation of these striae is ultimately due to the relative movement of 

 the air and the clouds under the influence of gravity and the laws of 

 hydro-dynamics; he rejects any influence of terrestrial magnetism or 



