2 Proceedings. 



the Austrian Tyrol, and Dr. SCHUSTER remarked that the 

 phenomena of such rock discharges had not been thoroughly- 

 investigated, and that records of such incidents would be 

 valuable. 



Professor OSBORNE Reynolds described a case of 

 " pitting " in the tubes of a boiler at the Owens College. 

 After being safely tested by a cold-water pressure of 3oolb., 

 one of the rust-pits gave way a few days later under a 

 steam pressure of only loolb. Beneath the crust of rust a 

 black deposit was observed. A discussion as to whether 

 this was a deposit of carbon from the iron, or black 

 magnetic oxide, ensued. A noticeable fact was that the 

 " pits " were most numerous at the smoke-box and not at 

 the furnace end, and that there (at the cooler end) the 

 lesion occurred. 



Mr. F. J. Faraday communicated a paper by Mr. 

 Frederick Hovenden on " The Study of Motes in Air," 

 in which the following experiment was described : — 



" Take a shallow glass trough, having a depth from back 

 to front of about % inch. Fill it with tobacco smoke ; this 

 will soon diffuse and the trough will appear filled with fog, 

 that is, the contained air will be charged with motes. Cut 

 a piece of cork and plug the mouth of the trough with it, in 

 order to prevent the escape of the motes and the dis- 

 turbance of air currents. Now, observe these motes by 

 means of the microscope, using the yi inch objective and a 

 parabolic condenser. Illuminate with a strong light — sun- 

 light, electric-light, or the oxy-hydrogen light. I have found 

 either of these lights to answer very well. The individual 

 motes will be seen, strongly illuminated, while the air- 

 atoms — the gases between the motes — are apparently in- 

 visible. The motes stand away from each other as if they 

 were separated by repulsion, or by something which is 

 invisible existing between them and separating them. 

 While the motes are thus divided each individual is in 



