60 ANNUAL OF SCIENTIFIC DISCOVERY. 



ited extent. The} 7 are durable, easily made, and have been made 

 to withstand a pressure of 400 pounds to the square inch. 



The pipes constructed of sheet iron, lined and coated exter- 

 nally with hydraulic cement, are said to be well adapted for dis- 

 tributing water where very cold weather does not prevail, frost 

 being inimical to the integrity of the pipe. So also is high pres- 

 sure said to be liable to injure the continuity of this kind of pip- 

 ing, especially at the numerous joints and connections. 



In England, pipe made of bituminized paper has been employed 

 in distributing both water and gas, but we have not heard that 

 it has become popular to any great extent. It also was attempted 

 to be introduced into this country, but without success, we be- 

 lieve. 



Another description of pipe is constructed of wood, being bored 

 from the solid log, lined with cement, and coated externally with 

 coal tar. This form of pipe is said to be extremely durable, 

 and, not being subjected to expansion and contraction by change 

 of temperature, is entirely free from leakage. 



In England and France, as well as in this country, the com- 

 plaints on this score are wide and deep, and a wide lield is open 

 for enterprise in introducing an especial remedy. 



TWIST DRILLS, AND RECENT IMPROVEMENTS IN THEIR MAN- 

 UFACTURE. 



We condense from a paper recently read, by Mr. G. Lauder, 

 C.E., before the Liverpool Polytechnic Society, the following 

 remarks upon twist drills : 



The last half century has witnessed many important improve- 

 ments in engineers' tools. Self-acting machines have been intro- 

 duced and improved, in numbers too great to mention in this 

 paper. 



The leading idea which seems to have controlled in all these 

 improvements is what has been designated the "guide princi- 

 ple." As examples, we may cite the slide-rest, the planing-nm- 

 cliine, etc., the objects to be attained being, first, greater accuracy 

 in the work performed, and, second, greater speed. in performing 

 it. 



After improved machines, which have enabled us to attain the 

 first object, we have to look to the forms of the tools used in these 

 machines, to^enable us to attain the second object, speed. 



Tools for cutting metals are divided into two classes, namely, 

 paring tools and scraping tools, these being distinguished by the 

 edge they present to the metal being cut. 



The data on which our knowledge of paring tools is founded 

 are altogether derived from practice in the workshop, workmen 

 themselves, he believed, having been, in a great many cases, the 

 leaders in improvement. The best cutting angle has been found, 

 for iron and steel, to be from 60 to 70, and Ithe angle of relief 

 3. 



Drills have been the last tools in common use by working en- 

 gineers to come under the whip of improvement, a large propor- 



