238 
The sum total of daily maximum sun temperatures at Giessen is 
much more nearly constant. 
In the Zeitschrift for 1882 Hoffmann gives the sums of the daily 
positive readings of his naked bright-bulb mercurial thermometer in 
the full sunshine; he also gives the sums of the temperature in the 
shade, and computes the average discrepancy or probable error of 
these numbers as deduced from their internal agreement year by year. 
He finds the probable uncertainty of the sums of maxima to be plus 
or minus | per cent and of the sums of shade temperatures to be plus 
or minus 10 per cent. ‘These latter sums relate to low-lying stations, 
such as Vienna and Dorpat, and these discrepancies diminish very 
much when we consider high mountain stations, where the shade 
temperatures of course give much smaller sum totals. He recognizes 
that the advantage of using the shade temperatures lies in the greater 
comparability of the observations made at different stations and with 
different instruments, but that the sunshine method is also greatly 
improved if the thermometers are perfectly similar and properly 
compared together, as in the instruments made by Doctor Ziegler at 
Frankfort. (See the report of the Senckenburg Association, 1879- 
1880, p. 337.) Hoffman’s observations with a variety of instruments 
convinced him that this difficulty as to instruments and exposures 
is not insurmountable. He collects comparative readings at several 
places and shows that the difference between the average tempera- 
tures in the sun and in the shade is larger at higher altitudes; thus 
at Giessen the average difference in summer at midday is 5° Réaum., 
and the whole range of the differences between sunshine and shade 
is from 3° to 15° Réaum. The corresponding average in the Hochge- 
birge, 7,000 feet, is never less than 8° Réaum. At the Bernina 
hospice, 8,113 feet, it is 25° Réaum. The average temperature of 
these mountain stations is 16.4° Réaum., corresponding to an elevation 
of about 6,000 feet. Similarly, J. D. Hooker observing a black-bulb 
thermometer in the sunshine in the Himalayas, found a difference of 
—15° Réaum. at 7,400 feet elevation, as contrasted with 4.4° at sea 
level. R.S. Ball, also using a black bulb, finds a difference of 18° or 
20° Réaum. in the Hochgebirge and of only 3° at Chiswick. 
These differences show the effect of the great dryness and mechan- 
ical purity of the air in the Hochgebirge. Hoffmann considers the 
smoke and clouds above us as affecting the difference between the sun 
and shade thermometers, but says nothing of the earth’s surface which 
completes the “ inclosure ” of the thermometer. 
The date from which Hoffmann begins his summation for Giessen 
is January 1; but as it would seem more proper to begin with some 
definite phase of vegetation, therefore he investigates the accuracy 
with which we can determine the initial phase and the effect of errors 
therein upon the ultimate sums. By painting the buds of certain 
