THE MAKEKSTOUN 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 influences, 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 



