E36 
NATURE 
[Fune 10, 1886 
month, and was at once set in action; the results of the pre- 
liminary trials when obtained being referred to a Committee 
consisting of the late Prof. H. J. S. Smith and Prof. Stokes, 
who, on July 5 following, submitted to the Meteorological 
Council a favourable report on the performance of the model. 
The Council at once resolved to have a machine constructed, 
which should be specially adapted to the requirements of the 
work for which it was intended, viz. the analysis of photographic 
thermograms and barograms. 
In preparing a working design for actual execution, it was 
found necessary to make several modifications in the details of 
the mechanical arrangements of Sir W. Thomson’s original 
model, and these were mainly worked out by Prof. Stokes and 
Mr. de la Rue. The construction of the instrument was in- 
trusted to Mr. Munro. It was considered sufficient to limit the 
action of the machine so as to extend only to the determination 
of the mean, and the coefficients as far as those of the third 
order, in the expression 
E =a + a, cos@ + sin 6 + a.cos 20 + 4,sin 26 + a3 cos 38 
+ é3sin 30 + &c., 
and to obtain these it was necessary to have seven sets of spheres, 
disks, and cylinders. 
A description of the machine, as actually constructed, together 
with engravings giving a general view of the machine, and 
illustrating some of its details, will be found in Engineering for 
December 17, 1880. 
The machine was delivered at the Office in December 1879, 
and a lengthened series of trials was at once commenced, to 
determine its constants, and thoroughly test the accuracy of its 
working, for which purpose systems of straight lines and 
curves, of which the values were known, were first used. A few 
small unforeseen difficulties were early met with, necessitating 
slight modifications in some portions of the instrument. 
The chief of these faults was a slight turning of the cylinders 
upon their axes, when the balls were moved to and fro along the 
disks, parallel to the axes of the cylinders. The movement was 
always in the same direction, namely, towards the disks, whether 
the ball was moved to the right or left. After the trial of many 
expedients the defect was finally, in great measure, overcome by 
attaching weights to the spindles of the cylinders. It however 
still exists in the machine to a slight extent, and its effect is to 
decrease the readings on the cylinders by a very small amount. 
It was decided to employ the analyser, in the first instance, in 
the determination of temperature constants, and careful com- 
parisons have been made of the results obtained by its means with 
those got by actual measurement of the photographs and numer- 
ical calculations, as will presently be mentioned, and the accord- 
ance is so very close as to prove that the machine may safely be 
trusted to effect reductions which could only otherwise be 
accomplished by the far more laborious process of measurement 
and calculation. 
It will facilitate an apprehension of the method of using the 
machine to give a somewhat detailed account of the operations 
involved in the treatment of the curves, with an example of the 
manner in which the readings of the machine are recorded and 
dealt with. 
The machine is furnished with three pairs of recording 
cylinders and disks, numbered consecutively 1 to 6, which give 
the coefficients for the first three pairs of terms of the expansion, 
and in addition a seventh cylinder and disk from which the mean 
is obtained. In the thermograms which supply continuous 
photographic records of the march of temperature, the trace for 
twenty-four hours covers a length of 8°75 inches, while a vertical 
height of about 0°7 inch! corresponds to a range of ten degrees 
in temperature ; each thermograph sheet contains the record for 
forty-eight hours. 
Conveniently placed in the machine is a cylinder or drum, the 
circumference of which is equal to the length of twenty-four hours 
upon the thermograms. Round this cylinder the thermograms 
are rolled, the fluctuations of temperature indicated by the curves 
being followed, as the cylinder revolves, by a combination of the 
movement of the cylinder with that ofa pointer moving in a line 
parallel to its axis. 
The handle by which the cylinder is turned gives motion at 
the same time to the seven disks of the machine, and the 
operator thus controls by his left hand both the speed with 
which the curves are paid through the machine and the conse- 
quent velocity of the angular motion of the disks, while, by a 
7 This value varies slightly for each observatory. 
stitable contrivance, the movements of the pointer, governed by 
his right hand and following the curve, produce on the face of 
the disks corresponding movements to the right or left of the 
balls by which the motion of the disks is conveyed to the 
recording cylinders. 
At the commencement of an operation all the cylinders are set 
to zero ; the twelve months curves are then passed consecutively 
through the instrument; the first pair of cylinders, which gives 
the coefficients of the first order, and also the mean cylinder, 
7, being read for each day, while cylinders 3 and 4, and 5 and 6, 
which give the coefficients of the second and third orders respec- 
tively, are only read for each five days and at the end of each 
calendar month. The numbers on the cylinders are, however, 
progressive, so that the increments upon them for any given 
period could very easily be obtained. : 
At present only the monthly increments of the readings have 
been dealt with, So as to obtain the coefficients of the mean daily 
variation for each month of the year. The process followed is, 
therefore, simply to divide the monthly increment by the number 
of days in the month, and then to multiply the quotient bya 
factor which is determined by the scale-value of the thermograms, 
and which will therefore be different for each observatory. 
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After some trials with the curves for the year 1871, the year 
1876 was taken up, inasmuch as for that year the records had 
been discussed by Mr. H. S. Eaton, F.R.Met.Soc., who had — 
calculated the hourly means of the various meteorological 
elements for each month separately, and who kindly placed his 
results at the disposal of the Council. 
The working of the machine was thus subjected to an exact 
test by comparing the results obtained by it with the coefficients 
in the harmonic series which were calculated from Mr. Eaton’s 
means ; and their trustworthy character, and the adequacy of 
these calculations to serve as a standard with which the coeffi- 
cients obtained by means of the machine might be compared, was 
established by calculating them from the odd and even hours, 
quite independently, for all the seven observatories. 
The outcome of this experiment was thoroughly satisfactory, 
and the entire series of results obtained both by calculation and 
from the machine was published as Appendix LY. to the Quarterly 
Weather Report for 1876, together with a Report prepared by 
Prof. Stokes, the concluding paragraphs of which may be quoted 
; here, since they sum up in a few words the conclusions 
arrived at. 
