326 
Agrimltiiral Meteorology. 
attention of those who possess any additional data for comparing 
the different rates of progress towards maturity made by the 
same plant under different meteorological conditions, so cas to 
reconcile the anomalies which now appear to exist. The whole 
study of the phenomena connected with the processes of germi- 
nation, foliation, flowering, and maturity, is extremely interesting. 
Some years ago the Academy of Bruxelles recommended the 
formation of an accurate record of observations,* embracing 
1. By observation of the quunlitxj of light we receive. 
2. By ditto of the solar heat received. 
3. By direct observation of the extent and mass of the clouds them- 
selves. 
The last method is obviously the least practically feasible, and would be 
by no means the most productive in its results if attained. The agricul- 
turist requires a measure of the (ffccts of the clouds at a given instant 
upon the transmission of light and heat. Now the same amount of these 
effects may result at different times from totals of cloud infinitely varied 
both as to their component masses, and their distribution over the liea- 
venly vault. This mass and distribution, supposing it could be accurately 
and easily determined for every given instant, is in fact a differential 
which we have no certain law for inteyratine/. And it is tlie integral which 
the agriculturist here requires. 
A comparison of the two other modes of observation for a given time 
would offer a complete measure of nebulosity in its integral effects. As 
regards the determination of calorific action, Sir John riersehel's actino- 
meter (since he has improved it by the insertion of an internal thermometer) 
offers advantages over Pouillet's pyrrheliometer, &c. M.Gasparin is pro- 
bably unacquainted with this perfected actinometer; and equally so with 
the actinograph (described in Art. VIIT. of Sir .John Herschel's paper, 
Phil. Trans., 1840, " On the Action of Light upon Preparations of Silica.'') 
This latter instrument includes ^hcliogrnph and nebidograph, worked by one 
and the same clock-movement. Mr. Jordan (mathematical and philoso- 
phical instrument maker. Sec, &c.) has further perfected the ap])]ication 
of the photographic principle to the purposes of accurate self-registration. 
The actinograph, with Mr. Jordan's ingenious scale added to it, would 
measure light to a numerical nicetv as complete as that of the actinometer, 
or other calorific instruments, and it possesses the great additional advan- 
tage of self-registration. 
This is not the place to enlarge upon the suggestions of Sir John Her- 
schel or others, towards the yet further applications which may be made 
of various principles {e.g. that of the cryophorus) for constructing mete- 
orological instruments of the utmost delicacy. The subject is a very exten- 
sive one, and would form an essay of itself, if treated with any approach 
to completeness. 
The present object is merely to suggest to M. Gasparin (and to other 
seientiiic agriculturists) how accurately the two instruments above named 
— the actinometer and actinograph (the latter having Mr. Jordan's scale 
added) — would supply the desired data, as regards light and heat. M. 
Gasparin seems to write unaware of the means which photography has 
offered towards the easy and delicate appreciation of degrees of nehidosity, 
and he would doubtless be the very first to estimate and apply the prni- 
ciple to this important purpose, since he dwells with peculiar and just 
emphasis on the deficiency hitherto. — -A. A. L. 
* Such observations require to be compared with the utmost care, and 
