58 Professor Forbes' s Experiments on 



bulbs in the legs are safety bulbs. For ammonia, &c, the 

 appropriate reagents are, of course, substituted. 



m 



tan 



^ 



Modification of Gahn's Blowpipe. — I employ a modifica- 

 tion of Gahn's blowpipe which is, perhaps, more convenient 

 in use, and more clean and agreeable to handle. A is a piece 

 of brass tube closed at the end, and having a boss near 

 the end perforated to admit the beak at a. B is the beak, 

 fitted to a by grinding, and bent at an angle of 135°, 

 which I find more convenient than a right angle for di- 

 recting the jet upward or downward by a little turn of the 

 beak without disturbing the support, and for minutiae in 

 operating. It can be turned in any direction. C is a piece 

 of glass barometer tube, fitted into A by binding round with 

 fine thread, and fixed with a little plaster of Paris : thus A 

 becomes the condensing chamber ; and when moisture is col- 

 lected there in so large quantity as to affect the beak, (but 

 which will never take place in a single operation, however long,) 

 the beak is withdrawn and the moisture blown out through 

 a. D is a bit of hard wood turned, and cemented round C; 

 where it serves as a stop to its entering A, and as a good hold- 

 fast in operating; the smallness of the tube in many blow- 

 pipes giving the fingers some difficulty in commanding them, 

 which occasions the preference felt by so many operators for 

 the blowpipe with a condensing bulb in the middle. 

 I am, dear Sir, yours very truly, 

 Plymouth, April 19, 1837. J- PniDEAUX. 



XII. Account of some Experiments made in different Parts of 

 Europe, on Terrestrial Magnetic Intensity, particularly with 

 reference to the Effect of Height. By James D. Forbes, 

 Esq., F.R.SS. L. Sf E., fyc, Professor of Natural Philosophy 

 in the University of Edinburgh.* 



1 . HPHE Council of the Royal Society of Edinburgh having, 



A on my application in 1832, entrusted me with Han- 



steen's magnetic intensity apparatus, in their possession, I feel 



* From the Transactions of the Royal Society of Edinburgh, vol. xiv., 

 having been read before that society December 19th, 1836. 



