632 Transactions of the American Institute. 



shades of the design, the electrical current is again established, 

 Hud the electro-magnet draws back, by its attraction, the graver 

 thus overcoming the force of the spring. It is easy to see how 

 comparatively plain work, like maps, could be executed with this 

 machine; but it is difficult to imagine how the depth of line in a 

 delicate copper plate is to be graduated by a graver governed by 

 one pair of electro-magnets. The multiplication of copies in this 

 plan is not as feasible as to duplicate the original plate by means of 

 the try-telescope process. 



SENSITIVE FLAMES. 



We have previously noticed the experiments by Prof. Tyndall, 

 of Loudon, showing the manner in which gjis flames ai'e affected by 

 sound. Mr. W. T, Barrett, lecturer on physical science at the 

 International College, who early made extended obsei'vations in 

 this direction, thus accounts for the phenomena. A sensitive flame 

 is one in which, on the slightest mechanical increase in the pressure, 

 or, what here comes to the same thing, in the velocity of the gas 

 as it issues from the burner, will change its shape and take very 

 much the appeanmce it has when influenced by sound. Now the 

 sonorous pulses excited by sound throw, among other things, the 

 pipe which conveys the gas to the burner into vibration; the flow 

 of gas is thereby driven from the sides and urged more toward the 

 center of the tube; and the current thus confuied, within narrower 

 limits, must issue from the burner with increased velocity so long 

 as the sound continues. It is the greater rapidity thus induced in 

 the issuing stream of gas which causes the flame to shorten and 

 diverge; lowering of the flame being an analogous effect to that 

 noticed and explained by Dr. Thomas Young, in his well known 

 experiments on streams of smoke ascending into the air at different 

 velocities. Several cases illustrating this action, and confirming 

 his opinion, are described by Mr. Barrett, in the April number of 

 The Philosophical Magazine. 



MOUNT HOOD, OREGON. 



The Rev. H. K. Hines has given to the Eoj-al Geogi'aphical 

 Society, of London, an account of his ascent, in company with 

 three residents of Vancouver, to the summit of Mount Hood. They 

 found that at forty feet below the summit water boiled with the 

 thermometer at one hundred and eighty degrees. He estimates the 

 height of Mount Hood at 17,640 feet, which is higher than any 

 summit in North America or Europe. The view from the top of 



