38 REPORT OF THE SECRETARY. 



period of the disturbance, and have also supplied a deficiency occasioned 

 by the loss of the registers of 1860 in the fire which occurred at the 

 Institution in 1805. For the purpose of exhibiting the extent of the 

 material in possession of the Institution, and to give credit to the faith- 

 ful and persevering observers who have so long gratuitously furnished 

 contributions to this branch of science, there is given in the appendix to 

 this report a full list of all the observers and of all the stations where 

 records have been made from the beginning of the year 1849 to the end 

 of 1808. The whole number of observers at present reporting to the Insti- 

 tution is about 400 ; of these 74 are furnished with full sets of instru- 

 ments. The number of observers under the direction of the army is 

 upwards of 100, of whom 50 are supplied with standard barometers and 

 other compared instruments. With this combined system, interspersed 

 with full sets of standard instruments, trustworthy data is obtained for 

 determining the general climatology of the country. It is true that 

 many of the instruments in use are not as perfect as could be desired, 

 yet they serve to indicate differences in the elements, and thus afford 

 the data for tracing the progress, as it were, of waves of atmospheric 

 pressure, and also of waves of changes in atmospheric temperature. 



Anticipating the important benefits which may result to our system 

 of meteorological obse?.- rations, particularly to those which relate to the 

 prediction of storms oji Hie Atlantic coast, we look forward with much 

 interest to the complel/jn of the Pacific railway. A well equipped 

 physical observatory placed at the highest point of the road, namely, 

 " Sherman's station," is very desirable, and we think it probable that 

 assistance from the railway company may be obtained to establish and 

 support an observatory of this character. 



During the past year a large number of rain gauges of a simple form, 

 such as were mentioned in the last report, have been procured and dis- 

 tributed to observers in various parts of the country. This gauge con- 

 sists of a hollow cylinder of tinned iron 2£ inches in diameter, and 12 

 inches in height, coated inside and out with varnish to prevent rusting. 

 The depth of rain is measured by inserting a graduated scale into the 

 gauge, and noting the height to which it has been wetted, in tenths and 

 pprts of tenths of an inch. The quantity of water in a fall of snow is 

 m^.sured by melting a column equal in diameter to that of the gauge. 

 This is obtained by pressing the gauge, mouth downward, through the 

 snow to the ground and isolating the contents by passing under the 

 mouth of the gauge a thin plate of metal. A rain gauge of this form, 

 after an experience of many years, is found to give the most satisfactory 

 results when used by ordinary observers. 



The discussion of all the material which we have collected in regard 

 to rain-fall, has served to point out the parts of the country in which the 

 registration is most deficient, and exertions have especially been made 

 to obtain observations from the great plains of the west and at the base 

 of the Rocky mountains. The great current of the return trade wind, 



