P OP ULAR MIS CELL AN Y. 



287 



very distant from those of the Zambesi, but 

 which soon takes a north and south direc- 

 tion. Only the upper course of this stream 

 was hitherto known to Europeans. It was 

 supposed that farther down it turned to the 

 west and flowed into the Atlantic as the 

 Owambo or Cunene. Pinto has now prob- 

 ably made the discovery that the Cubango 

 is a tributary of the Zambesi. However 

 this may be, our knowledge of the interior 

 of Africa has been considerably enlarged by 

 Pinto's journey. 



On reaching the Transvaal Territory the 

 explorer sent the following dispatch to the 

 King of Portugal: "I ain now six days' 

 journey from the Indian Ocean, and on the 

 point of completing my march across Afri- 

 ca from the west coast. I have struggled 

 against hunger and thirst, wild beasts, sav- 

 ages, floods, and drought, and have happily 

 surmounted all these obstacles. My records 

 are safe, and consist of twenty geographical 

 charts, three volumes of important coordi- 

 nates, meteorological notes, three volumes 

 of sketches, and a voluminous journal. I 

 have lost several men. Complete study of the 

 upper Zambesi, sixty-two cataracts and rap- 

 ids. Plan of the cataracts. The natives 

 fierce ; unceasing wars. The secret of the 

 Cubango. Serpa Pinto." 



Strength of Hard and Soft Steel. It has 



hitherto been supposed that a soft bar of 

 steel can longer resist the disintegrating 

 action of strains and shocks than a hard 

 one, but experiments made by W. Metcalf, 

 of Pittsburg, appear to prove the contrary 

 to be the fact. His attention was first called 

 to this matter by the constant breaking of 

 steam-hammer piston-rods. Made of ordi- 

 nary steel, they lasted but six months, an 

 iron rod lasting but half as long. Then 

 lower and lower steels were tried, and broke 

 in about five months. In an emergency, a 

 rod of comparatively high steel was em- 

 ployed, and this, which it was supposed 

 could not serve for more than a week or 

 two, held out for more than two years. This 

 result led Mr. Metcalf to investigate the 

 whole subject systematically, and a lot of 

 small steel connecting-rods were tested in 

 a special machine. The test required was, 

 that a machine should run 4-| hours at a 

 rate of 1,200 revolutions per minute, un- 



loaded, before the connecting-rod broke. 

 These rods were unforged in the middle, and 

 consisted of a piece of round bar with a 

 head welded on each end. " The mode of 

 rupture was," says Mr. Metcalf, " as a rule, 

 the same in all cases ; the rod heated at the 

 middle, where the vibrations met, as they 

 were imparted by rotary motion at one end, 

 and by reciprocating motion at the other, 

 and by alternating strains of compression 

 and extension. In some cases the rod be- 

 came slightly red-hot at the middle before 

 rupture. After heating, the next thing ob- 

 served was the raising or loosening of the 

 surface scale of the middle. Soon after this, 

 rupture began, first at the surface and grad- 

 ually extending to the center. The break- 

 ing was gradual in every case, no piece break- 

 ing suddenly, even of the highest steel. The 

 first trial was with "53 carbon steel: mean 

 time of six trials, 2 hours 9^ minutes. Sec- 

 ond trial, - 65 carbon steel : mean time of six 

 trials, 2 hours 57 minutes. Third trial, 

 85 carbon steel : mean time of three trials, 

 9 hours 45 minutes, and the trials were 

 stopped." A set of twelve connecting-rods, 

 made from special ingots, was then pre- 

 pared. These were tested with the follow- 

 ing results : 



The '30 C ran 1 hour 21 minutes, heated 

 and bent before breaking. 



The '49 ran 1 hour 28 minutes. 



The -53 ran 4 hours 57 minutes, broke 

 without heating. 



The -65 ran 3 hours 50 minutes, broke 

 at weld where imperfect. 



The '80 ran 5 hours 40 minutes. 



The -84 ran 18 hours. 



87 C broke in weld near the end. 



96 C ran 4 hours 55 minutes, and the 

 machine broke down. 



The whole twelve were not tested, because 

 the machine was needed for other works, 

 and, when Mr. Metcalf returned to complete 

 the experiment, it was discovered that the 

 foreman of the shop had picked up the un- 

 broken specimens, put them into machines, 

 and sent them off". Enough was done, how- 

 ever, to show that the maximum of strength 

 to resist vibration was not found among the 

 ductile steels. Mr. Metcalf gives some other 

 data concerning the performance of steel 

 suspension-rods in a bridge that corroborate 

 his views, which are practically novel. 



