556 



SCIENCE 



[N. S. Vol. XXVI. No. ( 



circuit is first broken. It will, However, soon 

 reach a state of equilibrium and remain near- 

 ly constant. 



The change in temperature required to make 

 and break the circuit varies with the form and 

 size of the regulator used and its contents. 

 In the mercury regulator constructed as rep- 

 resented in Fig. 1 it is less than one half 

 degree. In the regulator made as represented 

 in Fig. 2, containing glycerin and mercury, it 

 is less than one tenth degree. If air is sub- 

 stituted for glycerin, the regulator is still 

 more sensitive, but the temperature main- 

 tained varies nearly two degrees with extremes 

 in barometric pressure. Barometric changes, 

 however, affect the liquid regulators but very 

 little. If water and air are substituted for 

 mercury and air, the temperature variation is 

 slightly increased. 



The advantage of glycerin toluole and chlo- 

 roform over mercury lies in the fact that they 

 have a much higher index of expansion than 

 mercury and, at least glycerin and chloroform, 

 are much cheaper. 



Both forms can be made more sensitive, 

 (1) by increasing the length of the chamber 

 containing the mercury, glycerin or other sub- 

 stances, (2) by increasing the diameter of the 

 tube near the electric end so as to admit the 

 use of a longer lever, (3) by increasing the 

 ratio between the diameter of the tube and 

 that of its constriction. (A constriction can 

 be made use of in the glycerin regulator as 

 well as in the one containing only mercury.) 

 It will thus be seen that there is theoretically 

 no limit to the possible sensitiveness of these 

 regulators. 



A glass tube having an inside diameter of 

 7 mm., reduced to 2 mm. at the constriction, 

 was found. to be suitable for the construction 

 of these regulators. In making the constric- 

 tion the tube should be heated and rotated 

 until the walls fall in before it is drawn out, 

 so that they will become thick and the tube 

 will be strengthened at this otherwise weak 

 point. No special care need be exercised in 

 bending the tube; various other forms than 

 those represented will answer the purpose just 

 as well. 



Either form of the regulators described can, 

 of course, be used in connection with " heat- 

 ing coils," such as described by Professor 

 Mark or others, or in connection with incan- 

 descent electric bulbs. The latter are usually 

 furnished without charge by electric power 

 and lighting companies. They serve the pur- 

 pose fairly well, although some inconvenience 

 must be expected, owing to the liability with 

 which they burn out, unless several are used 

 in heating each bath. 



In case bulbs are used and apparatus is con- 

 structed with this in view, I think metal tubes 

 large enough to admit a bulb should be sol- 

 dered in the side near the bottom. If the 

 cylindrical form of bulb is used these need 

 not be large. The tubes should be dead black 

 inside and closed after the lamps are in. In 

 this way practically all the light energy is 

 transformed into heat energy. 



Heating with electricity is somewhat more 

 expensive than heating with gas. I was, how- 

 ever, surprised to find that a sixteen-candle 

 power incandescent lamp, with the circuit 

 broken nearly three fourths of the time, will 

 maintain a temperature between fifty and 

 sixty degrees in a well-insulated bath which 

 holds about one liter. S. O. Mast 



Johns Hopkins University 



seismographs in utah 

 It may be of interest to many to know that 

 seismographic apparatus has recently been in- 

 stalled at the University of Utah. The univer- 

 sity campus covers part of a shore terrace 

 built by the Pleistocene water-body known 

 as Lake Bonneville on the easterly outskirts 

 of the region now occupied by Salt Lake City, 

 and lying practically at the base of the Wa- 

 satch range. The Wasatch Mountains are of 

 immature age, and consequently are now 

 rising. Raw scarps at the foot of a spur just 

 northeast from the city, and similar scarps at 

 the base of the main range a short distance 

 to the southeast, tell of comparatively recent 

 up-slips of these sections of the mountain 

 mass. At the Wasatch base directly east from 

 the city, along the line of the bench-land junc- 

 tion with the mountain mass, there is little 



