406 TRANSACTIONS OF SECTION A. 
Mr. Burnside, however, solved the difficulty by devising a simple method ? 
whereby platinum wires may be sealed through Jena glass; according to the same 
method other conductors, such as copper wires, may be sealed through ordinary 
glass. 
The method consists essentially in fusing the metal and glass together in the 
usual way and then immersing the seal, after it has cooled to about a red heat, 
in a bath of oil or fat. Each immersion lasts about two or three seconds. The 
seal is immersed a little further in the cooling medium at each successive 
immersion until it is completely cooled. 
For currents up to 15 ampéres solid conductors may be employed, but for 
larger currents it is found advisable to make use of tubular conductors, which 
may be quite easily sealed through glass according to Mr. Burnside’s method. 
In preliminary experiments copper wires 1.5 mm. in diameter were success- 
fully sealed through German glass, and platinum wires of 1 mm. diameter were 
sealed through Jena and other glasses. A copper tube, capable of carrying a 
current of 100 amperes, was sealed through German glass. Platinum wires were 
sealed through Jena glass in mercury vapour lamps, and the seals were found 
to be air-tight after a period of over eight months, although they had from 
time to time been subjected to the heat of the lamps when burning. 
The chief advantages of this method of sealing electrical conductors through 
glass are as follows: (1) The process of obtaining seals is much simpler than 
any at present in use; (2) for incandescent electric lamps and all kinds of 
vacuum tubes, with the exception of mercury vapour apparatus, copper or other 
high conductivity metal may be used as the conducting material; (3) in the case 
of mercury vapour apparatus a minimum quantity of platinum is used in the 
tubular form of conductor for large electrical currents, because the tubular shell 
may be filled in with copper, subsequent to the sealing process; (4) conductors 
of very much greater cross-section than it has hitherto been possible to employ 
may be sealed through glass; (5) the one process is applicable to all kinds of 
glasses. 
9. Exhibition of a Seismograph. By J. J. Suaw. 
10. A Simple Method of determining the Period of Waves at Sea. 
By Dr. Vauauan Cornisu. 
Hitherto the method of determining the period of waves at sea from a ship 
on her course has been to note the interval between the arrival of waves at the 
bow or stern of the vessel, and the angle which the direction of their advance 
makes with the ship’s course. The speed of the ship being known, the true 
period can be calculated. 
During a voyage from Southampton to Colon and back in 1912 the author 
found that the true period of the waves can be quickly and accurately determined 
from the vertical oscillations of patches of spent foam, which are always 
numerous upon the surface of the sea except during absolute calm. With the 
aid of a stop-watch the interval is taken between the times when a patch of foam 
is borne upon the crest of successive waves. By this means it is not difficult 
to determine the period of the swell as well as that of the waves which are 
driven by the wind which blows at the time of observation. The post of observa- 
tion should be as high as possible above the water in order to discriminate more 
clearly between the shorter, steeper waves and the longer, flatter swell. 
The method is not only quicker than that hitherto in use, but has the 
important advantage that it obviates the necessity for observing the direction 
of advance of the waves, which is difficult to determine with accuracy. 
The following are examples of the measurements made by the author ;— 
May 28, 1912, average period of 28 waves, 2:095 secs., 
May 28, 1912, average period of 25 waves, 2°156 secs., 
the two sets being taken one immediately after the other. 
2 The Electrician, July 4, 1913. 
