OP ARTS AND SCIENCES. 533 



powerful quantity discharges which are more interesting from a scien- 

 tific point of view than discharges of high electromotive force ; for a new 

 field appears to be opened in spectrum analysis. Photographs of the 

 spectra of gases can be obtained with one or two discharges with a nar- 

 row slit. 



Perhaps the most interesting results obtained with the battery were 

 from the methods of exciting the X-rays. Photographs of the usual 

 subjects treated by these rays can be taken, and they exhibit great con- 

 trasts ; moreover, there are traces of ligaments and muscles as well as 

 bones. The members of the Academy visited the battery room and saw 

 a hydrogen tube excited by the discharge from three hundred Leydeu 

 jars, and the lighting of an X-ray tube. 



The following papers were presented by title: — 



Paleontological Notes V. A New Fossil Crab from the Mio- 

 cene Greensand Bed of Gay Head, Martha's Vineyard, with 

 Remarks on the Phylogeny of the Genus Cancer. By Alpheus 

 S. Packard. 



On the Thermal Diffusivities of Different Kinds of Marble. 

 By B. O. Peirce and R. W. Willson. 



Paleontological Notes VI. On Supposed Merostomatons and 

 Other Paleozoic Arthropod Trails, with Notes on those of 

 Limulus. By Alpheus S. Packard. 



On the Continuity of Groups generated by Infinitesimal 

 Transformations. By S. E. Slocum. Presented by Henry 

 Taber. 



On the Thermal and the Electrical Conductivity of Soft 

 Iron. By Edwin H. Hall. 



An Apparatus for Recording Alternating Current Waves. 

 By Frank A. Laws. 



The Dinitro Compounds of Paradibrombenzol. By C. Loring 

 Jackson and D. F. Calhane. 



On Certain Derivatives of Orthobenzoquinone. By C. Lor- 

 ing Jackson and Waldemar Koch. 



Geometry on Ruled Quartic Surfaces. By F. B. Williams. 

 Presented by W. E. Story. 



On the Action of Sodic Sulphite on Tribromdinitrobenzol and 

 Tribromtrinitrobenzol. By C. Loring Jackson and Richard B. 

 Earle. 



