May 8, 1903.] 



SCIENCE. 



749 



cavities. The use of the pneumatic chisel has 

 made it possible to remove the matrix from 

 such cavities, with but little injury to the 

 specimen. The tendency to chip off thin 

 edges with flakes of the matrix is also avoided. 

 Skill in the use of these tools is readily ac- 

 quired. By adapting the size of the chisel to 

 the work in hand and gauging the amount of 

 air admitted to the tool by means of a push- 

 button throttle valve, the stroke can be reduced 

 so that a scale may be removed from the most 

 delicate surface. 



E. S. ElGGS. 

 Field Columbian Museum. 



by the following formulae: 



F.° = § C.° 4- 32° = f E.° -f 32°. 



Fahrenheit degrees being plotted along a 

 horizontal axis, and Centigrade or Reaumur 

 degrees along a vertical axis, the graphs of 

 the two equations above give two straight 

 lines, as shown, from which, having given a 

 reading in one of the systems, the correspond- 

 ing reading in either one of the other two 

 may be obtained. 



Thus to find the equivalent of 80° R. the 

 horizontal from the 80° division on the ver- 



THERMOMETRIC HEADIXGS. 



Having had frequently occasion to transfer 

 thermometric readings given in one of the 

 common systems. Centigrade, Fahrenheit and 

 Reaumur, into one of the others, the accom- 

 panying diagram has been developed, which 

 affords a convenient and rapid means of such 

 transformation, and is adequate, provided a 

 high degree of accuracy is not desired. The 

 relations between the three systems are given 



tieal axis is followed to its intersection with 

 the line marked Reaumur, thence downward 

 where the corresponding Fahrenheit reading 

 (212° F.) is found on the horizontal axis; or 

 upward to ' Centigrade ' line and thence hori- 

 zontally to left where the corresponding Cen- 

 tigrade reading (100° C.) is found on the 

 vertical axis. 



Both lines cross the horizontal, or Fahren- 

 heit, axis at the same point, 32°; the Reaumur 



