[bovby] presidential ADDRESS 17 



having been subsequently eliminated, the experiments have been con- 

 tinued by Mr. Farmer, who has extended his researches to the investiga- 

 tion of the impact efficiency of jets impinging upon flat and curved sur- 

 faces. These results are presented in a paper at this meeting. 



In the course of these experiments observations were also made on 

 the phenomenon known as " the inversion of the vein," which Avas first 

 studied b}^ Bidone and subsequently by Magnus, Buft'and Lord Eayleigh. 

 The common explanation of this phenomenon is tbat the fluid particles 

 issuing along diflterent pai'abolic stream-lines impinge upon each other, 

 and by their mutual reactions cause the jet to spread out and assume 

 sectional forms depending upon the shape of the oritice. 



A theory \t-hich seems more fully to account for the whole of the 

 facts is that the peculiar changes in form are really due to surface tension 

 and to the differences between the atmospheric pressui'e and the internal 

 pressure of the jet. 



In the case, for example, of a jet flowing through an elliptical orifice 

 with the major axis vertical, the stream-lines in the vein are convergent 

 and mutually react upon each other, causing the jet to contract vertically 

 and elongate horizontally at a rate gradually increasing to a maximum, 

 when the section is a circle in form. 



At this stage the rates of elongation and contraction are the same. 

 The elongation and contraction still continue, but at a diminishing rate, 

 until the movement is stopped by the effect of surface tension, when the 

 section is again elliptical, with the major axis horizontal and the minor axis 

 vertical. The new major and minor axes then again begin respectively 

 to contract and to elongate, the section of the jet passing through the circu- 

 lar form to its initial elliptical form. 



This process is repeated over the whole length of the unbroken jet, 

 and, in fact, in this portion of the jet the surface tension produces an 

 effect similar to that which would be produced if the jet were surrounded 

 by an elastic envelope. 



The determination of the physical properties of materials of con- 

 struction offers a wide field for investigation. In the laboratories at 

 McGill University, results of considerable interest have been obtained as 

 to the magnetic properties of iron at high temperatures, by a new 

 method devised by Professor Callendar. A research on the thermo- 

 electric properties of iron and copper has been made with a view to the 

 accurate verification of the formulas of Avenarius and Tait. A new 

 electi-ical method of measuring the thermal conductivity of metals is 

 being tried in order to settle the much disputed question as to whether 

 the conductivity is constant or varies with the temperature. An attempt 

 is also being made to verify the very difficult experiments of Lord 

 Kelvin on the existence of the Thomson effect, and to measure the 

 amount. 



Sec. III., 1896. 2. 



