PALEONTOLOGY — PHYSICS. 363 



Another result expressible in general terms, but directly important, 

 bears on the use of fossil plants as cUmatic indices. Any Mesozoic 

 cycadeoids, or any other gjinnosperms leading into or toward the 

 early dicotyls, must have had much the same capacity for zonal dis- 

 tribution as present-day dicotyls and gymnosperms. There is there- 

 fore need for caution in viewing Cycadophyte floras as proof of uniform 

 tropic conditions. The view has long been current that from the late 

 Triassic throughout the Jurassic and Cretaceous, "there were no dis- 

 tinct polar, temperate, or equatorial zones," and that [essentially] the 

 same plants are found from within a few degrees of the poles all the 

 way to the equator. Here, too, old evidence must be reviewed, and 

 long-held opinions must evidently be revised. 



PHYSICS. 



Bams, Carl, Brown University, Providence, Rhode Island. Continuation of 

 investigations in inter jerometry. (For previous reports see Year Books 

 Nos. 4, 5, 7-17.) 



The peculiar behavior previously observed in treating the elastic 

 deformations of small bodies on the interferometer induced the author 

 to construct the contact lever, using achromatic fringes described in 

 the beginning of the report. The instrument at once functioned 

 admirably when employed either as a surface tester or as a spherometer. 

 This contact lever was then modified for the interpretation of the 

 elastic discrepancies specified, and the conditions shown under which 

 both the new and the old methods lead to trustworthy results. 



In a different application of the contact lever the small elongations 

 with subsequent contractions experienced by iron in magnetic fields 

 are treated. They are peculiarly interesting, because these phenomena 

 are at their maximum variation after the metal has become practically 

 saturated. Furthermore, an instrument which lends itself with equal 

 faciUty to the measurement of thermal expansion and of moduli is 

 in a measure self-contained for the solution of many thermodynamic 

 problems. 



Electrodynamometry of very weak {telephonic) currents. — No availa- 

 ble effect is obtainable, unless the vibrator of the measuring 

 instrument is sharply in resonance with the alternating current; then 

 the response is astonishingly large and definite. When the measure- 

 ment is made by the vibration telescope, the vibrator of the telephonic 

 system carrying the objective, the sensitiveness obtainable is not 

 beyond a few microamperes per ocular scale-part of reasonable value 

 (0.01 cm.). Within these limits, however, it may be made serviceable, 

 for instance, in determining the number of turns in each of a variety 

 of secondary coils, successively slid over the same long solenoidal 



