150 SCIENCE, 
the south, masks and often obliterates the mo- 
tion we seek to find. Again: such waves are 
frequently divided, then united, thus by the loss 
of their identity making it impossible to trace 
them for along period. One of the simplest 
methods of procedure in an investigation of 
this nature would be the projection of the ob- 
servations of temperature in curves, one for 
each station, and then studying the fluctuations 
from station to station. This was done by 
Professor Elias Loomis, in his ninth paper, in 
which he investigated the motion of waves of 
high and low pressure. 
An investigation of this kind, a short time 
since, gave 19.8 days for the mean interval 
of time of sixteen waves, moving from St. 
Michael’s, Alaska, to Turuchansk, Siberia, 
along the sixty-fifth parallel, or an approximate 
mean velocity of 15.8 miles per hour. Such 
a determination, however, cannot be regarded 
as entirely satisfactory, because it simply takes 
into account a series of stations lying in an 
east and west direction. 
In order to extend the investigation to a 
large number of stations, we may take daily 
‘departures’ from the monthly mean, and, pro- 
jecting these upon charts, determine the char- 
acter of the fluctuations over a large area. In 
practice, however, this method fails, for the 
reason that the fluctuations diminish toward 
southerly latitudes, thus masking the progres- 
sive motion. 
The following method has been adopted for 
obviating the latter difficulty. We may con- 
sider, that if a cold wave advance in any di- 
rection, without disturbance from dense clouds 
or mountain ridges, it will carry minimum tem- 
peratures to successive stations in its path; 
the intervals of time between the passage of 
such a minimum over any one station taken as 
a starting-point, and others in the line of prog- 
ress, gradually increasing. By determining, 
then, the time of passage of a minimum across 
each station in a country, and charting these 
times, we can ascertain both the line of advance 
and the velocity of the wave. 
In order to obtain the time of passage of a 
minimum temperature over a station, where 
a series of observations has been made each 
day, it is essential first to eliminate the effect 
of diurnal range. This may be done by ob- 
taining the residuals for each observation of a 
month, taken at any hour; then, determining 
the approximate time of passage, we can, by 
examining the successive residuals near that 
time, obtain the time sought. An effort has 
been made to apply the above principles to the 
observations of the U. S. signal-service, taken 
& 
(Vou. IIL, No. 5 3, 
five times each day during November, 1881, 
at forty-two selected stations. In this month 
there were four prominent cold waves ; and the 
following table gives the interval of time which 
elapsed between the passage of each of these 
over Fort Dunvegan, North-west territory, and 
each of the forty-two stations. ‘These figures 
are inserted exactly as determined from the 
observations. It was found, however, that 
many of the apparent discrepancies in a pro- 
gressive law of motion were due to the appear- 
ance of clouds at the time of an observation, 
thus throwing the minimum forward or back 
four and even eight hours. Blanks indicate 
that the minimum could not be determined 
satisfactorily. 
ao 
Coid waves, I., 1., 1I1., and IV., of November, 4 
I8s1. 
Hours between Fort Dunvegan 
and stations in U.S. . 
Station. . 
1 II. } IM..| IV. |Meam: 
J 
ass ; 
Ape nas Michi esis mmemie eres 32 52 64 49 , 
BismanckesD) aks emcee 24. 12 16 48 25 
Bostons Massey: amin cneeneee 64 52 60 OF 62 
Brownsville, Tex.. cee 48 64 32 64 by4 
Butialo.eNe yes ea) fa. Cone 36 56 48 76 54 
suveliaewora,s Wing o 6 a © °c 64 = - 72 68 
@ape Miaiyey Nise ue) e-em RAES 72 64 72 64 
Charlotte-wNE© jee 56 48 52 72 57 
Chattanooga, Tenn. 3: 32 48 40 56 44 
Cheyenne, Wyo. .... . - = 2, 28 | -20 
Cincinnati OF) ae een Oe 28 52 56 42 . 
Concho, Lex 9.) 7. oe is = rs, 48 | 40 : 
Davenport, Lon. ian ene, 24 3 48 32 ; 
Deadwood, Dak. = jes) alee 0 8 40 16 4 
Dodge City, Kan. . Ben) ae 8 12 32 21 { 
Eastport, Me. | 72 | 56 | (64 7 serena manag ; 
Paso lex) fas ence PSO 72 56 64 68 \ 
Fort Assinaboine, Mont. . ./| 24 Os 24 10 
Fort Buford, Mont. . . . .| 20 Om —a16 40 11 
Fort Elliott, Tex. . 32 | 16] 327 \NAgiaieee 
Fort Gibson, Ind. Ter. . 32 24. 28 56 35 7 
Galveston, Tex. ie 48 48 52 55 
Huron; Dak... < -cunae eS Sa iieas 32 16 
Key West, Hla.. 2° 5 a se lp Loe - - 76 70 
Kitty, Hawk, INC], seman eg oO 56 56 76 61 
Marquette, Mich... .. .j] 40 | 48 40 52 45 
Memphis; enniy =) jaune: 382 | 24 48 52 39 
Montgomery, Ala. . . . -j 06 - 56 76 63 
Moorhead, Minn... .. © | es 24eieage 0 48 24 
INew, Orleans, lias. enn eee 48 52 72 yi 
North! Platte, Nebr 9 see - 8 16 32 19 
New, York,JN ay.) oA) coe emer: 48 72 56 80. 64 
Omaha, Nebs- (45) fe - 8 24. 40 24 
IEatitisio io; ee is) a ene 52 56 48 48 51 
Ram taikvaiss),) Hild ee aene 48 - 84 72 68 
StiLouis Mol) sae eee 32 24 32 52 35 
Ste ann) Muaiainiye ccs eames 24 24 36 40 31 
Sti. Vincent; Minny a9). sien 24 16 UE 28 23 
Savana (Gals) wee 52 72 56 72 63 
Shreveport, Jua: 2) =e emer - - 32 52 42 
Toledo. O).,/. <3.) eu eee 28 30 52 76 | 46 
Washington, D.C. . . | 56 48 72 72 62 
Projecting the mean interval for the four — 
waves upon a chart (see accompanying plate). — 
ty 
