May 25, 1888.] 



SCIENTIFIC NEW^S. 



499 



diaphragm is movable and attached to a piston rod, 

 which passes through the top cover. To clean the 

 sponge an up-and-down motion is given to the lower 

 diaphragm or piston, thus alternately compressing and 

 releasing the sponge. These filters will render Thames 

 water at London clean enough for boiler-feeding or other 

 manufacturing purposes, at the rate of about 100 gallons 

 per square foot of surface per hour. The precipitate 

 resulting from the processes known as " softening " water 

 is now generally extracted by filtration. The material 

 used for this purpose is the filter-cloth referred to at the 

 commencement of the paper, as the chalk deposit may 

 accumulate to a considerable thickness before it becomes 

 impervious. In this case the deposit is easily removed; 

 the author finds that simple external jets of water are 

 sufficient for the purpose. 



EDINBURGH ARCHITECTURAL ASSOCIATION. 

 On May 3rd, Mr. Gilbert Goudie read a paper on " The 

 Brochs or Round Towers of Celtic Scotland." Proceed- 

 ing to describe these unique and remarkable structures 

 of remote antiquity, which had not previously engaged 

 the attention of any architectural body, and are not to be 

 confounded with the ecclesiastical round towers of Ireland 

 or of Scotland, Mr. Goudie submitted, as a typical 

 example, the broch in the island of Mousa, Shetland. 

 This, the best preserved of existing specimens, is still 

 standing to a height of upwards of forty feet. It is a cir- 

 cular tower consisting at first of a solid wall (unless 

 where pierced by three chambers formed in its thick- 

 ness). At the height of 8 feet this massive wall, hither- 

 to 15 feet thick, assumes the form of two concentric 

 walls, with an intervening space of about 3 feet, which 

 is converted into a succession of horizontal galleries six 

 in number — some of them about 5 feet high, and some 

 lower, immediately above each other — and intersected 

 by a staircase leading to the top. The central area is an 

 open circular court of about 30 feet diameter. The only 

 external aperture is the entrance — about 5 feet by 3 

 feet — passing through the main wall to the inner court, 

 from which the stair to the galleries ascends. The stair 

 and galleries are lighted by four sets of small rectangu- 

 lar window openings above each other looking into the 

 court. The walls are of very solid masonry, the stones 

 of good size without tool marks, and are dry built, with- 

 out lime or clay mortar. There is also some rude 

 buildings attached to the main wall on the inside, irre- 

 gular in form and undeterminable in object. These 

 architectural features described apply to broch structures 

 everywhere, with variations in size and in constructional 

 details in individual instances, foundations of large ramb- 

 ling buildings on the outside being very common. The 

 most laborious investigators of brochs have been Dr. 

 Joseph Anderson, the Rev. Dr. Joass, of Golspie, Sir 

 Henry Dryden, and the late Mr. George Petrie, who 

 have given measurements and collected a mass of infor- 

 mation regarding their structure and contents which 

 now enables us to treat the subject with some degree of 

 scientific accuracy. As regards the contents of the 

 brochs, the lapse of time since their erection and occupa- 

 tion has led to the destruction of what was most perish- 

 able within them, but there have been found numerous 

 querns or hand-mills, spindle whorls of stone, stone 

 cups, lamps, whetstones, occasional articles of bronze, 

 such as pins and tweezers, bone combs and pins, im- 

 plements of deerhorn, etc., all indications of an iron age 



occupancy. On one occasion in Orkney a slab bearing 

 an incised cross with an Ogham inscription was dis- 

 covered. Coming to the consideration of the origin of 

 the brochs, the architectural features of their construc- 

 tion were described as being essentially native and 

 Celtic, and so dissimilar to anything known in Scandi- 

 navia as to put out of court the contention of the late Dr. 

 Fergusson, author of the " History of Architecture," that 

 they were erected by the Scandinavians. The lecturer, 

 therefore, had no hesitation in asserting the theory which 

 assigned them to native builders, old Celts of Scotland 

 and the isles, in the pre-Scandinavian period terminating 

 more than a thousand years ago. They are now found 

 iu Orkney, Shetland, Caithness, Sutherland, and Ross- 

 shire, on the mainland and in the isles, but individual 

 instances remain so far south as in Perthshire, Stirling- 

 shire, and in Berwickshire, indicating that they existed 

 over the whole Celtic area in this country, though lapse of 

 time and agricultural improvements have accomplished 

 their almost total obliteration, except in the remoter dis- 

 tricts. It is thus in Scotland, and in Scotland alone, 

 that these structures are to be found. The brochs appear 

 to have been simply towers of defence, possessed 

 of large capacity for accommodation, though by no 

 means of a comfortable kind, and of almost unassailable 

 strengths in the then methods of warfare. The question 

 of the date of their erection is beset with difficulty. No 

 record of their erection or ordinary occupation is pre- 

 served. 



It has been advanced that the absence of reference to 

 brochs by Roman authors in treating of the Conquest 

 and partial occupancy of Caledonia, while such struc- 

 tures are known to have existed at one time in districts 

 with which they were familiar — e.g., the valley of the 

 Forth, where at least one example remains — is ground 

 for assigning their erection to an exclusively post-Roman 

 period — i.e., subsequent, say, to the fifth century. It is 

 also the fact that articles discovered in or associated 

 with brochs are usually of an iron age type, not 

 indicative of the highest antiquity. But, in the opinion 

 of the lecturer, great weight was not to be attached 

 to negative evidence of this kind. Their existence 

 might have been ignored by the Roman writers that 

 are known, and, with further systematic exploration, 

 evidence of earlier civilisation may at any time be 

 produced, the articles at present known being naturally 

 relics of later occupants. Some of the brochs were com- 

 pletely in ruin, and had become grass-grown mounds, 

 when Pagan interments, sometimes with cremation, 

 were made in them. Their destruction must, in any 

 view, have taken a prodigious time to accomplish, and 

 he was not disposed to confine their erection and occu- 

 pancy within any limitation of time that it was within 

 the power of existing knowledge to determine. 



«-j»i^>«^«t-» 



THE COUNTING OF DUST PARTICLES 

 IN AIR. 



'T'HE extreme importance of knowing about the nature 

 and number of the dust-particles in the air has now 

 been brought most prominently before physiologists and 

 physicists. Considerable attention has been recently 

 directed lo the computation of the micro-organisms in 

 suspension in different layers of air at different places ; 

 and the result of the work has already been very 

 successful. But till the other day no one has ever 



