65 
growth in experiments lasting 3'/, hours; that drawn in full repre- 
sents the growth in experiments of 7 hours. At and above 35° 
practically no growth takes place in the second period of 8'/, hours. 
In conclusion the temperature coefficient has been calculated for 
intervals of 10°, relating to the observations during 3'/, hours. 
We see, as has been indicated by ConeN Sruart') in his study of 
the subject, that van ‘tT Horr’s rule at most applies only over a 
small range; for the rest the coefficient falls with rise of temperature. 
Utrecht, April 1916. = Botanical Laboratory of the University. 
Astronomy. — “Determination of the constant of Precession and of 
the Systematic Proper motions of the stars, by the comparison 
of Kisrner’s catalogue of 10663 stars with some zone-cataloques 
of the “Astronomische Gesellschaft’. By C. pm Jone. (Com- 
municated by Prof. B. F. van Dr SANDE BAKHUYZEN). 
(Communicated in the meeting of April 28, 1916). 
1. Introduction. 
The research, the results of which will here be given in an 
abbreviated form, originated in a subject for a prize essay which 
the University of Leiden gave out in 1914, that of determining 
the constant of precession and the systematic proper motions by a 
comparison of KüsrNrr’s Catalogue of 10663 stars (Veröff. Bonn 
N°. 10) with Zone-Catalogues of the “Astronomische Gesellschaft”. 
The essay which [ wrote, was awarded the prize by the Faculty 
of Natural Science in Leiden. Prof. B. F. van DE SANDE BAKHUYZEN 
then suggested to me to continue the research and make it into a 
complete whole by using all the available material, i.e. that for 
which the difference of epoch with KüsrNrr is not too small, and 
reducing it in a strictly systematic manner; this suggestion I followed 
willingly. 
It is indeed of importance to derive the constant of Precession and 
the elements of the motion of the sun from the above mentioned 
material; it is the only combination of catalogues with at all con- 
siderable difference of epoch in which, for both, the magnitude-error 
has been eliminated or determined with sufficient accuracy. For the 
zone-catalogues of the Astr. Ges. two determinations of the error in 
1) C. P. Conen Stuart. A study of temperature coefficients and van ‘rt Horr’s 
rule, Proc. Kon. Akad. van Wet. Amsterdam, 1912. 
5) 
Proceedings Royal Acad. Amsterdam. Vol. XIX. 
