236 
quency is injurious, inasmuch as the cloudiness cuts off the influence 
of sunshine. The fact that years of low temperature are always 
years of poor erops is a fact that must be generally considered as a 
local phenomenon because of the simultaneous conpensation as to 
temperature that is continually going on in contiguous localities. 
HOFFMAN. 
Prof. Dr. H. Hoffmann published, first at Giessen and afterwards 
in the Memoirs of the Senckenberg Association at Frankfort (Vol. 
VIII, 1872), the details of a work which he began in Giessen in 1866 
on the relation between the development of plants and the tempera- 
ture recorded by a maximum thermometer in full sunshine. Some 
account of that work and its subsequent continuation at Giessen is 
given in successive papers published in the Journal of the Austrian 
Meteorological Association (Zeitschrift O. G. M.) during the years 
1868 to 1891. The detailed references to these will be found in the 
list of papers appended to this present report. Hoffmann’s first 
conclusion, as stated in 1868, was that he had found a precise, intel- 
ligible, and comparable expression for the quantity of heat that is 
needed for the attainment of any definite phase of vegetation. He 
would take the sum of the daily maxima of a thermometer fully ex- 
posed to the sunshine. His first work at Giessen was done with a 
naked glass bulb, self-registering, mercurial, maximum thermometer, 
graduated to Réaumur’s scale, attached to a wooden frame and set 
out in full sunshine 4.5 French feet above the soil or green sod in an 
open portion of the botanic garden at Frankfort. The exposure was 
indeed not perfectly free, but was such that the sun shone upon the 
thermometer from sunrise to 2 p.m. in January and until 4.30 p. m. 
in June. Hoffmann’s summations begin with midwinter, or January 
1, and he gives the sums of the positive daily maxima (1. e., above 
0° Réaum.) up to the dates of leafing and flowering for 10 plants. 
Apparently preliminary values are given in the Journal of the 
Austrian Meteorological Society for 1868 and 1869, but final values 
in the memoir published at Frankfort, 1872. 
In the Meteorologische Zeitschrift for 1875 Hoffmann says that 
after four years’ work at Giessen (1866-1869) his thermometer was 
broken. A new one was constructed by Dr. J. Ziegler, of Frankfort, 
in accordance with their mutual understanding; this had a mercurial 
bulb, but was very many times larger than the former, and therefore 
very much more sluggish. Observations with such instruments, 
graduated to accord with the Réaumur scale, were begun in 1875 by 
Hoffmann at the botanic gardens at Giessen, and by Ziegler at the 
gardens at Frankfort. In order to compare these two series together 
and to unite them with the earlier Giessen series the ratios of the 
sums as given by the earlier and the later thermometers for the same 
