106 =. Loomis—Observations of the U. S, Signal Service. 
these changes. Nos. 3, 6, 8, 9, 13, 15, 18, 19, 20, 25, 27, 28, 29, 
30, 33, 34, 35, 37 and 38 were apparently of this kind. 
e maps accompanying the Hamburgh Review for January, - 
1877, clearly show that No. 7 of the cases on page 101 belongs 
to this class. I have no information which enables me to judge 
of the other European cases on page 101. 
The cases of barometric minima enumerated in the table on 
page 103 were all accompanied with high winds and some of them 
with violent winds; they were generally accompanied with a 
great fall of rain or snow, and the rain-area generally extended 
to a great distance in front of the storm’s center; but the most 
noticeable circumstance which characterizes all the cases is the 
great extent of abnormal winds in front of the storm’s center. 
ese abnormal winds were apparently due to an area of high 
barometer situated on the south, southeast, east or northeast 
side of the low center. These winds (in consequence of the 
rotation of the earth) tend to produce a depression of the bar- 
ometer on their left side. They were generally accompanied 
with a considerable rain-fall, which tends to increase the 
velocity of the winds and thus produce a greater depression 
of the barometer. 
In order to illustrate more clearly the operation of these dif- 
ferent causes, I have prepared Plate IV, which shows the isobars 
and winds for January 15, 1877, at 4.385 p. mM. (case No. 31 of 
the table on page 103). We see that the center of the low area 
ment due to these causes would soon cease if there were no 
recruiting force. This force is supplied by the precipitation of 
the vapor which is present in the air. When this vapor is con- 
ak the neighboring air rushes in with great force to de an 
the place of the condensed vapor, and the air is expanded by 
the latent heat which is set free. This cause is sufficient to 
maintain high winds as long as there is a great precipitation of 
vapor. 
On Plate IV the direction of the wind is indicated by arrows; 
and the force of the wind is indicated by the number of feathers 
attached to the end of the arrows. One feather indicates 4 
