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Notes 2795 barrel and the surrounding liquor, but large enough to permit ready flow between them when desired. The pipet is fitted at the top with an ordinary glass stopcock, leaving a mouthpiece of glass about 2.5 cm. above the cock. Its total length is not longer than a stirring rod.The sample to be analyzed is secured in a beaker, diluted suitably, and indicator added if necessary. The portion is adjusted when possible to require a set amount of standard solution. The stirring rod is introduced and the barrel filled. The pipet stopcock is closed and the standard solution run into the beaker as rapidly as possible from the buret to a slight excess, the buret stopcock being full open until the end-point is signaled. The pipet meanwhile functions as a stirring rod. Half of the withdrawn barrel portion is now drained into the beaker and titration repeated to excess, this time by additions of say twenty drops each. This cycle is repeated with say five drop portions. The rod is then rinsed in the solution by running liquid in and out several times. The final titration in one drop portions is rapid. The color variation or other indication of the end-point is fresh in the memory. Judgment is not strained. It was found even when duplicates were being run that it was quicker and easier to titrate by this method. A medicine dropper arrangement is similar but not satisfactory. It is not precise and not readily cleaned.If the sample can be adjusted approximately to require a set volume of standard solution the titration (with a set procedure) will always occur in a fixed time.

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The magneto-telluric field, in the spectrum 8 s to 100 min, has been recorded at four stations, Eskdalemuir (lat 55"17' N, long 3"ll' W), Portpatrick (54'51' N, 5"S W), Port Erin (54'5' N, 4"45' W) and Nefyn (52'56' N, 4' 33' W). Records of E were obtained simultaneously on two short cables orientated N-S and E-W at Eskdalemuir, the H variations being obtained from the observatory records there. At the other stations E was recorded on six cables (9-120 km long), five of which cross part or all of the Irish Sea. The measurements were made on each cable in turn. At each station the component of H orthogonal to the cable was also measured.Assuming a top layer of resistivity 3000 ohm-metres, the profiles at Eskdalemuir indicate a thickness for this layer of 12 km. Underlying this is a layer of resistivity 45 ohm-metres which extends to a depth of 30 km ; beneath this the resistivity is about 2500 ohm-metres. These results do not depend critically upon the resistivity assumed for the top layer.After corrections have been made for the estimated thickness and resistivity of the sediments in the Irish Sea, the results from five of the six long cables confirm the presence of a low resistivity (10-100 ohm-metres) layer in the middle or lower part of the crust.On comparison of the magnetic field records with the magnetograms of Eskdalemuir observatory, it was found that, although the shape of the pulsations was similar at all stations, the amplitude ratios between stations showed considerable dependence upon the period of the oscillations. This can be explained largely by anomalies in conductivity near Nefyn and Port Erin. It appears unlikely that sedimentary basins in the Irish Sea can account for more than a small part of the anomalies.The effect of finite dimensions of the source is discussed ; corrections for a possible variation of the field dimension have been made and it is found that these do not materially affect the results.Possible induction effects of the Atlantic Ocean have been considered and it is concluded that these have been negligible in this survey.

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Microseisms in the frequency band 4 to 100 c/s, commonly encountered in seismic prospecting, have been investigated in various parts of England, urban and rural. A diurnal variation in background level, indicating man-made sources, was found everywhere within 2 miles of a major road or community. The main sources were found to be traffic, heavy machinery, aircraft, wind and rain, with traffic prevailing. In rural areas at night-time a steady background of about 10 -6 cm/s r.m.s. particle velocity was found, with occasional superimposed activity lasting 4 to 30 s. The latter has been shown mostly to be local and of geophysical origin, the precise nature of which is unknown. Various possible causes are discussed, both of this and of the minimum background.