If the apparatus could be attached to a storage battery on which there were no other loads, it would be comparatively easy to get closer regulation by using a narrower range of current variation. The battery used in these experiments is liable to have other loads thrown on at any time. The curves (Fig. 2) show the variations plotted from the tables.

Next the existence of a vertical temperature gradient was examined. Readings on thermometer were made at different levels and no sure difference of temperature was observable when the space inside heater is empty. When masses of metal or other obstructions were placed inside, slight differences amounting to one thousandth of a degree were observed. In experiments like this all the windows in the apparatus must be covered as radiation causes noticeable differences in temperature.

The platinum thermometer led to another important discovery. Even after the automatic controlling apparatus becomes steady it was found that the temperature of the air inside the heater continues to rise. This is due to the fact that altogether the wall of the heater box is about 1.8 cm. thick and while the mean temperature of the mercury in the wall does not vary, the temperature of the inner part and the wall adjacent to it is rising while that of the outer part is falling. This rise may amount to more than .1° and it is a matter of an hour or so before it disappears. This time has been shortened by placing a small flat heating coil of fine GS wire along the inner wall inside. A small current sent through this helps to establish equi

librium a little more quickly. Considerable judgment must be exercised in its use however.

Finally the effect of the stirring system was investigated and it was found that running at normal speed, the fans gave a rise in temperature of about .1° per hour; so that any slight variation in speed of fans is not important, but great variations may interfere with close regulation.

The ease with which one temperature after another can be obtained is one of the features of the apparatus. Other advantages are the wide range of available temperatures, the precision with which any given temperature may be reached and maintained, the large volume of heating chamber, ease of observation and the certainty of operation. Another advantage in work near the critical point is the small amount of damage caused by explosion. The windows, which are easily replaced, may be blown out but no injury to the essential parts has ever occurred and explosions have not been infrequeat.

QUEEN'S UNIVERSITY,

KINGSTON, ONTARIO.

Proceedings of the American Academy of Arts and Sciences.

VOL. XLVIII. No. 16.- MARCH, 1913.

CONTRIBUTIONS FROM THE PHANEROGAMIC LABORATORIES OF HARVARD UNIVERSITY.- No. 59.

CRETACEOUS PITYOXYLA FROM CLIFFWOOD, NEW

JERSEY.

BY RUTH HOLDEN.

WITH FOUR PLATES.