284 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 12 



in (1) the interpretation and detailing of information for specific craft in 

 fiight; (2) the dispatching of craft; (3) the furnishing of information to other 

 departments of the concern; and (4) the instruction of pilots. 



Governmental activities must be expanded along lines of the collection of 

 aerological information. With this assistance, the general flying weather 

 forecasts will probably keep pace with the development of the demand. The 

 making of upper air pressure maps is the type of research problem of great 

 assistance in forecasting. The status of this problem was discussed. The 

 work of the commercial meteorologist can be surmised by reference to charts 

 of upper air conditions along flying routes. This paper has appeared 

 in full in the Monthly Weather Review. 



L. H. Adams and E. D. Williamson: The density of strained glass (illus- 

 trated; presented by Mr. Adams.) 



The stresses existing in "strained" glass are such that in the interior portion 

 of the glass the density is less than that of unstrained (annealed) glass, while 

 in the outer portion it is greater. It can be demonstrated, however, that in 

 any strained piece of glass these two efi"ects exactly neutralize each other, 

 so that the total volume of the piece is unaffected by strain. In order to 

 reconcile this conclusion with the experimental results which always show a 

 smaller density for strained glass when compared with unstrained glass, it 

 is necessary to assume that the apparent diminution of density is due to the 

 formation of bubbles in the interior, where a hydrostatic negative pressure 

 exists. This agrees with the conclusion reached many years ago by Barus 

 that the low density of Prince Rupert's drops is a consequence of the presence 

 of vacuum bubbles. 



G. T. Rude : The tidal work of the Coast and Geodetic Survey (illustrated) . 

 Tidal work of the Coast and Geodetic Survey had its origin in the necessity 

 for reducing soundings, in hydrographic surveys, for the fall and rise of the 

 tides. The needs of the engineer and mariner have necessitated the extension 

 of the work until now it covers the following fields: Prediction of tides and 

 preparation of annual tide tables; determination of datum planes; develop- 

 ment of instruments for observing and predicting tides; study of mean sea 

 level and its relation to crustal movements; and the study of tidal phenomena 

 in general. 



The issue of tide tables for the use of the mariner began in 1853 with a 

 condensed table for eight stations for the United States. These tables have 

 increased in size and scope so that now they appear annually, in advance, 

 as a volume of about five hundred pages covering the entire maritime world, 

 with full predictions for each day of the year at eighty-one principal ports 

 and tidal differences for more than thirty-five hundred subsidiary ports. 

 Prior to 1882 the tides were predicted by means of empirical tables and 

 graphs. Beginning with that year the predictions were made on a machine 

 designed by Mr. William Ferrel of the Survey. This machine was essen- 

 tially a maxima and minima machine and in 1910 it was replaced by a new 

 tide-predicting machine designed and constructed in the office of the Survey. 

 On this new machine the height of the tide at any time between high water 

 and low water is indicated, and the time and height of the tide are indicated 

 on the face of the machine, from which they can be recorded directly on 

 forms for the printer. The setting of the machine and the prediction of tides 

 for a full year at any station require about ten hours. 



It is, of course, out of the question to predict the tides for all ports. To 



