THE MAKERSTOUN OBSERVATIONS. 
7 
Mr Welsh shared in all the work of observing and computing. A large 
mass of observations of the new planets were made with your large equatorial, 
chiefly by Mr Welsh, at extra-official hours ; these observations have been pub- 
blished by the Royal Astronomical Society. 
Mr Hogg shared in the regular and disturbance observations, assisted in the 
computations, and performed all the mechanical work connected with the obser- 
vatory and its instruments. 
I have already noticed, in different Introductions to the Makerstoun Observa- 
tions, the diligence and care of my assistants. I shall here repeat my obligations 
to Mr Welsh, who was trained from the commencement under my own eye. His 
acquaintance with the mathematical details of his work, his skill as an observer, 
his fidelity in all he performed, and his appreciation of the practical difficulties 
occurring, have been of the greatest importance to me. He was made conversant 
with all my own views upon the theoretical and practical questions which so often 
developed themselves, and, in return, I frequently derived considerable benefit 
from his opinions. 
To Mr Hogg, also, I can award my testimony as to the honesty and diligence 
with which he has fulfilled the duties for which he was at first engaged. To his 
invention and handicraft most of the mechanical contrivances, in wood and 
brass, about the observatory are indebted. 
Suggestions. — I shall now offer a few suggestions, the results of my expe- 
rience, on the subject of magnetical and meteorological observatories, especially 
in such climates as our own. 
Situation. — I need scarcely say that it is of importance, especially for abso- 
lute magnetical determinations, that the position chosen for the observatory should 
not be over highly ferruginous rocks, even though observations can be made in 
the neighbourhood to determine any local error. But there is a point connected 
with the placing of magnetical and meteorological observatories which it seems 
to me is of very great importance, a point which has been apparently overlooked 
to a very great extent ; I mean the influences due to the proximity of large 
cities. These hifluences, I fear, are much greater than may be suspected, 
and that not only on the absolute values, but likewise on the variations, 
whether magnetical or meteorological. Suppose an observatory placed on one 
side of a large city, which contains immense masses of iron, huge piles of stones, 
and thousands of human beings ; this combined mass has a temperature several 
degrees higher than that of the air at a distance ; it is a generator of electrical, 
thermal, and aerial currents : have these no effects upon the magnetical and 
meteorological states of the neighbouring district ? The probabilities appear all 
in favour of an answer in the affirmative, and, at least, till the negative can be 
