178 REPORT—1896, 
that either an east and west or a north and south line could be used at 
pleasure. 
The result of the observations made so far is to suggest that the method 
has certain advantages over others which have been used elsewhere. 
1. The long focus gives a large image on which much minute detail 
can be seen, and affords a large displacement for a small angle and the 
best opportunity of selecting accurately corresponding points on the 
two negatives. 
2. The image of the sun as a fixed point of reference is completely 
reliable. 
3. The observation of the time is easily made, can be made with 
exactness, and is the only precise observation required at the time of 
exposure. 
4. There is no possibility of misunderstanding between the two 
observers. 
_ 5. The share of work falling upon the assistant observer is extremely 
simple. 
6. The shortness of base diminishes perspective difficulties and allows 
the use of a smaller site. 
It has, however, one great disadvantage, it cannot be applied to clouds 
which do not come near enough to the sun to be in the same field of view, 
nor to clouds which completely hide'the sun. This, however, could easily 
be got over by providing each camera with altitude and azimuth circles, 
of which the former need only be graduated from the zenith to the horizon, 
while the latter should be complete. They should be provided with 
verniers reading to 2’ of arc. Telephonic communication between the 
two stations would also be a convenience, but its absence has only been 
felt occasionally when things have gone wrong. 
Nearly a hundred pairs of exposures have been made, not counting 
many experimental observations, but all these have not yet been worked out. 
The following table gives the heights so far determined. They are 
given in yards and miles, the latter being offered for comparison with the 
Kew results. 
Date | Time Yards Miles Cloud 
W. MM. 
| April1l7 , -|, 12 45pm). 3,736 213 Broken fragments of cu- 
he hs gir is eed Qdieliin Ieyad 982 2°26 } mulus. 
May8 . ah 410 838 “47 Base of cumulus. 
iY : oH 415 995 “56 Side of cumulus. 
af ; ‘ 415 1,950 1:10 Top of cumulus. 
Maylt . : 10 OA™M.| 6,330 3°59 Cumulo-stratus. 
BS ; - |} 10°20 7,575 4:30 Cumulo-stratus. 
rs ra 4 10 P.M. 2,592 1:47 Stratus. 
= sail 415 2,478 1:40 Stratus. 
May 15. - | 1 £0 3,358 19 Cumulus forming. 
ca : - | 4 20 1,782 1-01 Cumulus disappearing. 
May19 . - | 2005 Aue! © 425525 1:43 Cumulus forming top. 
* S ose eLON2 1,394 79 Cumulus forming base. 
May 22 . ogee) Ley, 7,708 4°38 Stratiform cloud forming. 
a - | 3 OPM. 5,847 3°32 Stratiform cloud disap- 
| pearing. 
June2 , A 3 20 10,288 5°84 Alto-cumulus forming. 
5 r SH 3 20 12,530 712 Mackerel sky, massing 
F » a 3.28 12,772 T25 | into high stratus. 
