Aprh,, 1911. 



KNOWLEDGE. 



135 



The Erection of the Ohservatokv at 

 Sax Lriz. 



The construction and the installation of the 

 obser\ator\- has been rapid and without any mis- 

 fortunes. In September of 1908 we commenced the 

 construction of the building of the observatory in 

 the grounds of the State school. The National 

 Go\ernment gave facilities for acquiring the area 

 necessarv for the observatory and for a house. Five 

 months later all was established ready for the 

 installation of the instruments, and for lodging the 

 members of the commission. 



After the preliminarv examination and the deter- 

 mination of some instrumental corrections, we 

 commenced the obser\ations for the scheme in the 

 month of April, 1909. 



It is the first occasion upon which an instrument 

 of this class has been erected upon artificial stone, 

 made with Portland cement, grit, sand, or fine gra\-el. 

 and strengthened with iron. 



The two large piers which support the axes 

 of the instrument are joined into one base extended 

 two or three meters, and this base, of two meters in 



depth, is fixed with the foundaticn, which is extended 

 beyond the base of the piers ; thersfcre, all is as one 

 block by this modern method of ccns'cruction. The 

 height of the pillars, with the b^ise, extends to five 

 meters above the foundation, which is of sand and 

 other materials. 



There are also two piers of the same construction 

 for auxiliary instruments in the largi room, and 

 another pillar at a distance of one hundred meters, 

 for indicating the meridian mark. 



The two astronomical clocks are installed within 

 a small room constructed for the work rooms ; each 

 clock is arranged on an artificial pillar of the same 

 concrete material. 



This is the histor}" of the Observatory of San 

 Luiz. No one here speaks of a work being in pro- 

 gress; it is an act almost completed. 



Up to the present we have verified more than 

 sevent\"-five thousand observations ; according to 

 this, five thousand per month since the beginning 

 of our project. 



As all has gone off well until this day, we may hope 

 that the work will be completed within a year from 

 the date of 1910. June 30th. 



QUERIES AND ANS\VER.S. 



Readers arc invited to scud in Questions and to ansK'cr the Queries zi'liicli are printed on tliis page. 



(JL'ESTIOXS. 



32. THE GENUS LIXARIA.— Is it possible to obtain a 

 complete list of the species and varieties of the genus Linaria ; 



if so where, and at what price ? 



G. K. W. 



33. "HALLEV'S COMET."— In the March issue of 

 " Know'Ledge " it is stated that Halley's Comet is still 

 visible ; and of about the 14th magnitude. 



Can any of your readers inform me whether the distance of 

 the comet from the Sun can be found by calculation at any 

 particular time, and also whether its speed can be determined ? 



As an example, how far will it be from the Sun, and how 



man.\- miles will it move a day, two years after passing 



perihelion, that is, on April 19th, 1912 ? , 



'^ , , f , Interested. 



34. ORIEXTATIOX OF THE GREAT PYRAMID.— In 



the articles on " The Great Pyramid " contributed by Proctor 

 to " Knowledge " Vol. I., he lays great stress on its careful 

 orientation, and devotes considerable space to the method of 

 obtaining a true north-and-south line by means of the 

 descending passage pointing to a Draconis and the ascending 

 passage equally inclined towards the south ; but he makes no 

 mention of the means of obtaining a true east-and-west line 

 which must also have been necessary for the construction, 

 perhaps because there is nothing to show what method was 

 actually used. Could a true east-and-west line be laid out by 

 observing a suitable star near the eastern horizon shortly after 

 sunset, and the same star near the western horizon shortly 

 before sunrise ? If so, between what latitudes is this method 

 available, and what considerations must be taken into account 

 in selecting a suitable star ? What other methods, astronomical 

 or otherwise, are likely to have been available to the Pyramid 

 builders ? 



REPLIES. 



24. DREAMS. — Much observation leads me to believe that 

 a large majority, at the very least, of dreams are instantaneous, 

 occupying only an infinitesimal part of the moment of returning 

 consciousness from sleep, and that a noise which wakes a 



sleeper is itself the cause of the dream which fits it. That, 

 in fact, the dream is an instantaneous " snap-shot " of a 

 commingling of subconscious impressions with those due to 

 external objectives. We must, most of us, be aware how 

 frequently a mere dozy shutting down of the eyelids is pro- 

 ductive of a \ery definite panorama of the mind. 



While in dreamland I may say that I doubt strongly the 

 occurrence of the repetition of the same dream in successive 

 slumbers, except as an exceedingly rare event. I believe that 

 the dream itself furnishes the thought of the supposed first 

 dream. Has anyone ever made a note of a dream, and then 

 referred to it when the repetition is believed to take place ? 



L. J. 



30. FINDING THE TIME BY THE HEAVENLY 

 BODIES. — For (II The determination of the time would 

 depend on the solution of a spherical triangle connecting the 

 hour angle, i.e., the time, with 5, a and ^, the declination and 

 altitude of the sun, and the latitude of the place, a being the 

 angle which has for its tangent the ratio of the lengths of the 

 stick and its shadow. The result might appear rather complex 

 to anyone unfamiliar with spherical trigonometry, and some 

 calculation with trigonometrical tables would be required to 

 obtain numerical results. 



The solutions of (2) and (3) are very simple. (21 requiring no 

 calculation, and (3) only the determination of a single angle 

 from the known value of its tangent. Generally if X is the 

 latitude of any place, and i and 5 the altitude and declination 

 of the Sun at noon on any date, then 90' — X = ct — 5 is always 

 true. 



For (2) X = 52 ; a -45; therefore 5 = 7°. The dechnation 

 of the Sun will be very nearly 7' at noon in London on April 

 7th and September 5th. 



For (3) a will be the angle which has for its tangent the 

 ratio of the length of the stick to the length of its shadow, and 

 the latitude of the place will be 90'— a + 5. 



The declination of the Sun can. of course, be obtained for 

 any date from the Nautical Almanac ; the sign before S must 

 be reversed if the Sun has South declination. J. H. G. 



