436 London, Edinburgh and Dublin Philosophical Magazine. 



perseverence, and a cautious application of general principles to 

 particular results,) to some of the most important and interesting 

 triumphs of mechanical and physical science. The paper of Profes- 

 sor Airey is on the " Diffraction of an annular aperture," a point 

 which he states has been " passed over too lightly by writers on the 

 undulatory theory." The problem is enunciated, worked out, and 

 proved, with the usual skill and acumen of that profound and accom- 

 plished mathematician. 



In the numbers of the Journal under consideration, are con- 

 tained no less than six communications from different observers, on 

 the electrical phenomena connected with Steam. This, being a sub- 

 ject which has very recently been made known, and, we believe, 

 accidentally discovered, has excited considerable attention in Europe 

 and elsewhere, as well as directed many experimental inquirers to 

 institute researches with a view to its elucidation. The value of 

 steam, in every point of view, and the daily increasing interest and 

 importance of the phenomena of electricity, as applied to practical 

 purposes, render them well worthy of the labour bestowed upon their 

 investigation. 



In the first paper of Dr. Schafhaeutl, " On Steam considered as a 

 conductor of electricity," he concludes from certain experiments detail- 

 ed, that steam, pure and free from contact with water, is a non-con- 

 ductor, resembling in this respect, the gases. He appears to ascribe 

 the electricity of steam to its condensation, on the rapid expansion 

 of which when issuing from a jet, its production in some measure 

 depends. In the same number, Mr. Armstrong of Newcastle, details 

 some interesting experiments on the same subject. He insulated the 

 boiler, and then ascertained that a jet of high pressure steam contains 

 little more electricity than one of low pressure, its apparent excess 

 being caused by its being more readily collected. He infers, that, the 

 electricity is in a neutral state while the steam is confined within the 

 boiler, and that it is a tolerable conductor of electricity " even in 

 its transparent state." The discrepancy in the results of these two 

 observers, shews, that many more experiments are required before any 

 definite conclusions on the subject can be arrived at. 



Mr. Armstrong appears to have been the first person who noticed 

 and attempted to explain these phenomena ; one of their chief uses will 

 be to enable us to understand many meteorological phenomena, con- 



