= 
Sree 
Method of ascertaining Distances. 271 
esporvi in questa memoria confermano sempre piu l’esistenza 
di un potere magnetizante nella luce, principalmente nel jembo 
estremo del raggio violetto, e la probabilita che questo potere 
appartenga piuttosto ai raggi chimici o disossidanti, che allo 
stesso raggio violetto.”—Dr. Morrichini thus concludes, page 32, 
his interesing memoir: ‘* The chemical and violet rays are never 
separated, and the intensity of the violet rays may proportionally 
announce those of the chemical. Terrestrial bodies may absorb 
from the solar rays the magnetic fluid as they absorb light and 
calorie, which two fluids are concerned in their decomposition and 
recomposition. Iron then may be with regard to the magnetic 
fluid what pyrophorus is with regard to caloric, and natural 
phosphori with respect to light.” This beautiful discovery may 
be said to throw a new light upon light. 1 regret that from 
previous arrangements [| had to leave Rome, before I could wit- 
ness the repetition of the experiment, on the first favourable day, 
and to which Professor Morrichini was so good as to invite me. 
Dr. Morrichini informed me, as the result of a series of very de- 
licate experiments, that he had constantly found the violet ray 
positive, and the red ray negative, with respect to electricity. 
From a series of experiments now in progress by the Professor 
of Botany at Rome, it would seem that violet light possesses a 
considerable influence in vegetation. 
I have the honour to be, sir, 
Your very obedient and most humble servant, 
J. Murray. 
XLV. Method of ascertaining Distances from one Station to 
another (in Levelling or Surveying) on Level and variously 
inclined Surfaces, to their exact Length of Horizontal Base, 
by the Addition of an angular Bubble attached to,the Tele- 
scope of a Spirit Level. By Mr. Joun Hueues, of Wal- 
worth *,’ 
Mode of adjusting the Bubble. 
Borisr A (fig. 2, Plate III.) to be the spirit leve?. HI,a 
quay, a wall, or any other level plane chosen for this purpose, 
on which are measured with great precision (say) four chains. 
BC, a horizontal line or visual ray, pointing from the telescope 
to the five-foot mark ou the levelling-staff F G, and correspond- 
ing in height with the fine wire, or spider’s s fibre, within the tele- 
scope. DE£ is a visual ray also pointing to nine feet on the staff 
(the telescope being thus elevated by means of the thumb screws); 
and while in that direction, the angular bubble must be screwed 
and so adjusted that it may stand exactly horizontal without re- 
‘ 
* Communicated by the Author. 
gard 
