192 SCIENCE IX SHORT CHAPTERS. 



an open mouth of measured area say 100 square inches. 

 This receives the rain that falls. By means of a pipe the 

 water is conveyed to a vessel having a surface of say one 

 square inch. By this arrangement, when sufficient rain has 

 fallen to cover the surface of the earth to the depth of one 

 hundredth of an inch, the little vessel below will contain water 

 one inch in depth. By balancing this vessel at the end of a 

 Jong arm, it is made to preponderate gradually as the weight 

 of water it receives increases, and finally, when filled, it tips 

 over altogether, empties itself, and then rises to its starting 

 place in equilibrium. To the other end of this arm a pencil is 

 attached, which inscribes all these movements on the revolv- 

 ing paper, and thus tells the nistory of the rainfall. The line 

 is zigzag while the rain is Jailing, and horizontal while the 

 weather is fair. The amount of inclination of the zigzag line 

 measures the depth of rain by means of the same ruled lines 

 on the paper as measure the height of the barometer, etc. 

 Every time the measuring vessel tips over a perpendicular line 

 is drawn, and the pencil resumes its starting level. The 

 papers containing these autographs of the elements may, of 

 course, be kept, as permanent records for reference whenever 

 needed, or the results may be tabulated in other forms. 



There are many modifications in the details of these self- 

 registering instruments. In some of them photography is 

 made to do a part of the work. The above description indi- 

 cates the main principles of their construction, without attempt- 

 ing to enter upon minute details. 



Meteorological observatories are provided with these instru- 

 ments, and all nations worthy of the name of civilized co-oper- 

 ate with more or less efficiency in providing and endowing 

 such establishments. They are placed in suitable localities, and 

 communicate with each other, and with certain head-quarters, 

 by means of the electric telegraph. One of these head- quar- 

 ters is the Meteorological Office, at No. 116 Victoria Stieet, 

 Westminster, S.W., which daily receives the results of the 

 observations taken at about fifty stations on the British Islands 

 and the Continent. The chief observations are made simul- 

 taneously at 8 A.M. and telegraphed in cipher to London, 

 where they usually arrive before 10 A.M. As they come in 

 they are marked down in their proper places upon a large 

 chart, and when this chart is sufficiently completed, a con- 

 densed or abstract copy is made containing as much informa- 

 tion as may be included in the small newspaper charts. This 



