NEW SEISMOGRAPH

New Zealand Times, Volume L, Issue 11435, 3 February 1923, Page 5

NEW SEISMOGRAPH

A DELICATE INSTRUMENT HOW THE SCIENTISTS “FISH FOR EARTHQUAKES.” INSTALLATION AT KELBURN. “What wo are all aiming at is being, iiiile tt;o > vrctl'iA oarlhquau.es» stated Dr. Adams (Government Astronomer) to a “Times” representative who interviewed him yesterday nrteinoon at Kclburu Observatory, alongside whir’ll preparations are now being made for the installation of a new seismograph, or “earthquake detector,” as it might he called. “Before wo can hope to do that, however, wo have to follow the ordinary scientific course, by proceeding to collect precise date of what is happening in the earth. We, therefore, need a delicate instrument which will at once record and measure all tho thrusts, strains, tremors, and quakes that take place; and by studying thousands upon thousands of these records, measuring and comparing them with infinite care, we may hope to be able at length to say that such and such a record means that an earthquake is due within a longer or shorter period of time. That is why we are now preparing to install alongside the observatory a Milne-Shaw seismograph—that is to say, a Milne seismograph as improved by Mr J. ,T. Shaw. This is the machine recommended by the chief British seismological authority. We had tbe machine installed temporarily at the Victoria College for exhibition at tlie Science Congress: but a. permanent .home is to be built for it here at (he observatory. That big pit you saw being dug beside the door of the observatory’ is for a concrete block or pillar, 12ft high, on which the seismograph will rest, so as to he free from mere surface vibrations.”

FORTY TIMES MORE SENSITIVE. Showing our representative a number of the daily records mado by the maohinje at Victoria College, Dr. Adams stated that it is forty times as sensitive as the old Milne machine, which was previously the only seismograph we had in New Zealand. “The result is,” he said, “that working with the new machine is like working with a microscope forty times more powerful than you have been used to working with. You will note (comparing the records) that the records of the old machine show only a straight line till a distinct quake is registered ; but the new machine shewn a serrated line, like the teeth of a small saw, demonstrating that the crust of the earth is in constant motion. That is to say, there are incessant minute oscillations of the ground. You will note, too. at larger or shorter intervals, a movement of the whole line to one side or the other by about its own width. That seems to indicate a sideways thrust, easing off when tbe lino eomes into position again.” A VERY SENSITIVE INSTRUMENT. “And what is that big jump of about a quarter of an inch, first to one side and then to the other,” asked our representative. ‘That,’ ’ replied Dr. Adams, “registers where I stood first at one side of the machine and then at the other. That shows how extremely sensitive the machine is, though its foundation is supposed to bo quite isolated from the floor of the room. On January 22nd, Anniversary Day, you will note a. distinct earthquake was recorded. From the oscillations shown I should judge that it wa3 some considerable distance away, possibly in the direction of Tonga, where we get a lot of earthquakes. Tlie one machine, however, can only indicate ' the radius within which tlie earthquake occurred not its direction, north, east, south, or west, as the case may he. The direction will not be obtainable until a second machine, mounted at right angle® to the first, is available. PHOTOGRAPHIC RECORDS. “11l the case of the new machine the tremors are recorded photographically by a beam of light, reflected on a particularly sensitive mirror and then thrown back on to a recording drum, covered, with bromide paper and revolving in a light-tight box or camera. Thbre is thus no friction in tho recording of the movements, such as is inevitable when tlie record is made by means of a pen on a revolving drum When we -have accumulated a large number of these records wo shall be able to study and compare them, so as to understand what they mean in the way of changing thrusts and stains and various movements of the earth’s cnist; and we liopo that gradually this study of the records will lead up to our being able to predict both when and where earthquakes are coming. Tho record slips of bromide paper nre changed once a day, each slip wound round the drum giving ns a iecord for the-whole twenty-four hours. Then the records have to be developed like any other photograph. It is very interesting, in fact, in its way, exciting work. You know what it is to go fishing, with what excitement you wa-tdh your line or rod for an indication of a nibble or a bite. Well, I watch the development of the records for a tremor or a ’quake, with just as much excitement lis a fisherman watches his line or his rod. It is, in a way, fishing for earthquakes.”