4 C. Bar us — Change of Heat Conductivity on, 



system is completely surrounded by a cylindrical box ABC, 

 through the hollow walls of which the water continually circu- 

 lates. In this way an environment of any constant tempera- 

 ture is obtained. 



To heat or cool the lower plate EE, it is made the top of a 

 shallow box EE, the bottom of which is perforated by influx 

 and efflux tubes G, G' . §7. 



The whole system, ABC, is heavily jacketed with blanket- 

 ing (not shown), and a sink placed below the efflux tubes car- 

 ries off the water. 



4. Environment. — This consists of the three parts AAA, 

 BB and CCCC, made of heavy tinned sheet iron, and capable 

 of moving up and down and of being clamped in any vertical 

 position along four upright slides (not shown). It is advisable 

 to fix the bottom CCCC permanently, and the frame is pro- 

 vided with leveling screws so that the plates DD and EE may 

 be adjusted to the horizontal, accurately. 



The top AAA is virtually a bell jar. Water enters at a in 

 jets directed toward the center as well as toward the right 

 (tangentially) so as to kee}3 up a circulation. It issues at b, 

 and passes thence through a sufficient but short length of 

 jacketed rubber tubing to the tubulure c, near the bottom of 

 the ring BB. Rotation is here also kept up by tangential in- 

 flux, and the water issuing at d near the top of BB, passes 

 through rubber tubing to e on one side of the bottom CCCC, 

 finally leaving this vessel at f on the other side. When not 

 otherwise used, the water is carried to a level above AAA, to 

 prevent siphon age. By making the environment of parts in 

 this way, two advantages are secured : for apart from the greater 

 thoroughness of circulation favorable to constancy of tempera- 

 ture, the parts may be raised so that the plates DD and EE 

 may at all times be easily charged or inspected. In the actual 

 apparatus the influx and efflux tubulures are to be in a vertical 

 plane at right angles to the thermometer tubulures. AAA 

 has four other tubulures : j (oblique) for the insertion of a 

 thermometer into the circulating water, and M for registering 

 the air temperature within ; through L the air which always 

 accumulates from hot water may be discharged, and through 

 N, a wire may be inserted for raising and suspending the 

 upper plate DD, §8. Similarly the tubulure k admits a ther- 

 mometer into the water circulating in BB. Finally the bot- 

 tom CC has two large and two small perforations, through 

 which pass the tubes G, G', and gg, as well as the wires of the 

 thermo-couple, §6. The tubulure ii reaching nearly to the 

 top, discharges accumulated air. 



5. Copper conduction plates. — Both DD and EE are silver 

 plated, making them less subject to the action of thymol. The 



