28 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 2 
zero, the temperature where the wire enters the air is 0.18 @, and the 
heat carried away by 2 leads in 3 minutes is 0.037 6, calories. For 
110 volts and 1 ampere the systematic error of such an arrangement 
with the heating coil running at 120° would be about 1 per mille, and 
the coil must heat less than 3° to safely avoid systematic error in work 
of 0.1 per mille precision. By doubling the length of lead in the in- 
closure the permissible heating is increased, somewhere near 8 times. 
A doubling of » would have an identical effect, but would be rather 
hard to secure with the same size of wire. It therefore seems that it 
would generally be very desirable to insert portions of finer lead wire 
next the coil, using enough larger wire further out, but well within the 
calorimeter, to dissipate to the calorimeter the heat generated in the 
fine wire. Advantageous dimensions can be calculated from the data 
already given. The insertion of too much copper resistance gives 
the heater resistance too great a temperature coefficient. There is 
little danger of trouble from this cause, however, as long as its possi- 
bility is not overlooked. 
The assumption of temperature equality between calorimeter and 
jacket, used in this section, is justified as follows: The temperature 
distributions and flows existing at any time are the resultant of the 
electric heat and of the jacket-calorimeter difference, and may be 
resolved into components due to these different sources. Since by 
a well known principle the resultants of such components can be ob- 
tained by simple addition, and since the results of the calorimeter- 
jacket difference are taken care of in the regular procedure, we may 
treat the electric effects alone, as if the others were non-existent. 
BOTANY.—The genus Microstaphyla.|. Winutram R. Maxon, 
National Museum. 
Among the many diverse ferns comprising the tribe Acrosticheae 
of the family Polypodiaceae one of the most interesting of all is the 
diminutive plant of St. Helena first described by the younger Linnaeus 
in 1781 as Adiantum furcatum, and later by Jacquin as Osmunda 
bifurcata. By the older writers it was placed at one time or another in 
no less than seven different genera, before serving as the type and sole 
species of Microstaphyla Presl. This, like so many other of Presl’s 
genera, was submerged in synonymy by later writers. In 1895 a 
closely related Bolivian plant, with simple instead of pinnate sporo- 
1 Published by permission of the Secretary of the Smithsonian Institution. Re- 
ceived November 29, 1922. 
