September 7, 1905] 



NATURE 



465 



pipes of the Pretoria district. This paper is of special 

 interest. In the Premier pipe a remarliable bar of purple 

 quartzite, locally known as floating reef, occurs. It 

 appears to be a mass of Waterberg sandstone that has 

 dropped into the pipe. The blue ground is considered to 

 be a serpentinised peridotite breccia with a specific gravity 

 of 2-757. That of the Kimberley blue is 2734. 



OVR ASTRONOMICAL COLUMN. 

 Discovery of a Nov.*. — A telegram from the Kiel 

 Centralstelle, dated September i, announces the discovery 

 of a new star, by Mrs. Fleming at Harvard, on August 12. 

 Its position, referred to the equinox of 1900, is given as 

 follows : — ■ 



R.A. = 284° 2' =i8h. j6-im. 

 Dec. = -4° 34', 

 and, although the magnitude is not mentioned, the Nova 

 is said to be fading rapidly. 



The position given above is near to that of \ Aquil^, 

 the Nova apparentlv forming the ape.\ of an equilateral 



triangle which is completed by A and 12 Aquila;. The 

 accompanying chart of the surrounding region shows the 

 approximate position of the object. 



A later telegram from Prof. Pickering gives the value 

 R.A. = iSh. 57m. 8s. as being more correct for the right 

 ascension of this object. 



W.^TER Vapour in the Martian Atmosphere. — In 

 Bulletin No. 17 of the Lowell Observatory, Mr. Lowell 

 describes a new spectroscopic method for testing the 

 presence of water vapour in the atmosphere of Mars, and 

 Mr. Slipher discusses the results obtained from an experi- 

 mental trial of the method. The principles involved are 

 as follows : — Cosmically considered, the earth's atmosphere 

 is at rest as regards a terrestrial observer, whilst the Arean 

 atmosphere partakes of the planet's motion relative to the 

 earth. This relative motion should be reflected in the solar 

 spectrum, as obtained on a spectrogram of Mars, by a 

 displacement of the lines due to the selective absorption 

 common to both atmospheres. But in the terrestrial atmo- 

 sphere water vapour accounts for a great deal of this 

 absorption ; therefore, if water vapour also exists in the 

 Martian atmosphere the lines due to it should show a 

 displacement, or at least a broadening, of such lines as 

 those in the a band of the solar spectrum, or, with small 

 dispersion, an extension on one side or the other of the 

 band itself. The spectrum of the sunlight reflected by the 

 moon, the approach or recession of which is negligible, 

 is taken as the comparison spectrum, in which the earth's 

 atmospheric absorption appears alone. 



Mr. Slipher obtained several spectrograms of Mars and 

 of the moon, the exposures being made when the re- 

 spective bodies were at the same altitude. An examination 

 of the a band and of the water vapour lines near D in 



NO. 1S7I, VOL. 72J 



both spectra seemed to indicate a slight shift, but the 

 measurements made were uncertain and discordant, and 

 no definite conclusion could be arrived at. So far as 

 selective absorption is concerned, the spectrum of Mars 

 seems to be the same as that of the equally high moon. 

 Similar experiments on the planet Venus, using direct sun- 

 light for the comparison spectrum, were equally in- 

 conclusive. 



Real Paths of Lyrid Meteors. — The real paths of 

 forty April meteors, recorded during the period 1889-1903 

 by different observers, are given by Mr. Denning in the 

 Observatory (August). Many of the objects observed were 

 Lyrids, and Mr. Denning emphasises the importance of 

 this shower and its contemporaries, and, further, gives 

 a daily ephemeris for the Lyrid radiant, based on his own 

 observations of 703 meteors (186 Lyrids) during the years 

 1873-1904. This ephemeris covers the period April 15- 

 April 25, but its author is doubtful of the radiant's activity 

 on April 15, 16, and 25. On April 15 the computed posi- 

 tion is = 263^°, 5 = 33°, and the latter value is constant. 

 The right ascension, however, increases at the uniform 

 rate of one and a quarter degrees per day. 



Observations of Satellites. — In No. 4035 of the 

 Astronomische Nachrichten Dr. C. W. Wirtz publishes the 

 results of a series of observations of various satellites 

 made with the 49 cm. (about I9i-inch) refractor of the 

 Strassburg Observatory during 1902, 1903, 1904, and 1905. 

 The results are given in a tabulated form, showing the 

 differences between the calculated and observed position 

 angles and distances. Dealing with Neptune's satellite. 

 Dr. Wirtz found that it exhibits a marked variation of 

 apparent brightness according to its position in its orbit. 

 In longitude 40° (or position angle 60°) it is brightest, 

 in longitude 240° {i.e. position angle 180°) it is least 

 bright. Saturn's satellites, iii.-viii. inclusive, are also 

 dealt with, the positions with regard to the planet and 

 then to each other being given. 



r//E BRITISH ASSOCIA TION. 



SECTION G. 



engineering. 



Opening Address by Colonel Sir C. Scott Moncrieff, 



K.C.S.I., K.C.M.G., R.E., LL.D., President of the 



Section. 



Science has been defined as the medium through which 

 the knowledge of the few can be rendered available to the 

 many ; and among the first to avail himself of this know- 

 ledge is the engineer. He has created a young science, the 

 offspring, as it were, of the older sciences, for without them 

 engineering could have no existence. 



The astronomer, gazing through long ages at the heavens 

 and laying down the courses of the stars, has taught the 

 engineer where to find his place on the earth's surface. 



The geologist has taught him where he may find the 

 stones and the minerals which he requires, where he may 

 count on firm rock beneath the soil to build on, where he 

 may be certain he will find none. 



The chemist has taught him of the subtle gases and 

 fluids which fill all space, and has shown him how they 

 may be transformed and transfused for his purposes. 



The botanist has taught him the properties of all trees 

 and plants, " from the cedar tree that is in Lebanon even 

 unto the hyssop that springeth out of the wall." 



And all this knowledge would be as nothing to the en- 

 gineer had he not reaped the fruits of that most severe of 

 all pure and noble sciences — the science of numbers and 

 dimensions, of lines and curves and spaces, of surfaces and 

 solids — the science of mathematics. 



Were I to attempt in the course of a single address to 

 touch on all the many branches of engineering, I could 

 do no more than repeat a number of platitudes, which you 

 know at least as well as I do. I think, then, that it will 

 be better to select one branch, a branch on which com- 

 paratively little has been written, which has, I understand, 

 a special interest for South Africa, and which has occupied 

 the best years of my life in India, Southern Europe, Central 

 Asia, and Egypt — -I mean the science of irrigation. My 



