March 21, 1878] 



NATURE 



405 



keeps moving. Besides this, the beam is not level, and 

 it is not in a convenient place. We want a horizontal 

 beam of light, and some means of keeping it in one place 

 all day. An instrument that will enable us to do this, 

 and that can be adjusted to the position of the sun in the 

 sky at all seasons of the year and every hou^r of the day, 

 may be readily made, and will cost only a small" sum of 

 money. 



We give several drawings giving different views of such 

 an instrument and some of its separate parts. It is 

 called a heliostat, and we shall find it of the utmost value 

 in our experimenting in light, heat, sound, electricity, 

 and other branches of physical science. 



Fig. I. 



The first drawing represents a front-view of the helio- 

 stat. The second drawing gives an end-view, and we 

 can now make one by simply following these few direc- 

 tions : The part marked A in the two drawings is a piece 

 of pine board, 23 inches (58"4 centimetres) wide and two 

 or more feet long, or as long as the window where it is to 

 be used is wide. Any boy who can use plane and saw 

 can make this piece of work out of common inch-board, 

 and, if you have no pieces so wide as that, it can be 

 made of two or more pieces fastened together with cleats ; 

 but, in this case, all the cracks must be close and tight. 

 In the middle of this board, cut a round hole 5 inches 

 (127 centimetres) in diameter, with its centre 8 inches 



from the bottom of the 'board. In the first drawing this 

 hole can be seen at B, and in the second drawing it is 

 shown by dotted lines at B. On one side of the board 

 screw two iron brackets, using brackets measuring 1.4 

 inches (35 "5 centimetres) by 12 inches (30'5 centimetres). 

 These brackets are placed one on each side of the hole 

 in the board, and are placed 14 inches (35 '5 centimetres) 

 apart, and with the short arm of the bracket against the 

 board. In the first drawing the two brackets are shown, 

 and rn the second drawing one is shown in profile, and 

 they are marked C in both drawings. On the end of the 

 brackets is placed a fiat piece of board, 6^ inches (i6'5 

 centimetres) wide and 14 inches (35*5 centimetres) long, 

 or long enough to reach from one bracket to the other. 

 This board may be screwed up to the brackets, and thus 

 make a shelf. Care must be taken in fastening this shelf 

 to the brackets to place it so that the outside edge of the 

 shelf will be 16 inches (40'6 centimetres) from the large 

 board. On the outside edge of this shelf another board, 

 7 inches (17 '8 centimetres) wide, is placed upright, and 

 secured with screws and small strips of wood at the ends, 

 as in the drawing. This shelf, with the wooden back, is 

 marked D in the drawings. 



These things make the fixed parts of the heliostat, and 

 we have next to make the movable parts, or the machinery 

 whereby it can be adjusted to the movement of the sun 

 in the heavens. First, get out a flat piece of board 10^ 

 inches (267 centimetres) long, 6| inches (16 centimetres) 

 wide, and \ inch (12 millimetres) thick. Then make a 

 fiat, half-round piece, shaped like the figure marked G. 

 This piece must be \ inch (7 millimetres) thick, 5^ inches 

 (14 centimetres) along the straight side, and with the 

 circular part with a radius of 3 inches (7'6 centimetres). 

 A hole, I inch (j:2 millimetres) in diameter, is made in 

 thisj as represented in the drawing, and then the half-round 

 piece must be screwed to the flat piece of wood we just cut 

 out. In the part marked N in Fig. i you will see these two 

 pieces fastened together. The piece marked i is the most 

 difificult piece of all. It should be made of ash or some 

 hard wood. One end is square, and has a deep slot cut 

 in it ; the rest is round, and may be i^ inch (32 milli- 

 metres in diameter. The square part must be large 

 enough to slip over the ha^f-circular piece, G, as is shown 

 at H. A hole, \ inch (12 millimetres) in diameter, is cut 

 in the two ends, as marked by dotted lines at J, and 

 through these holes an iron bolt and nut are fitted, so as 

 to hold the circular piece, G, and yet allow it to turn freely 

 in every direction. A hole, if inch (32 millimetres) in 

 diameter, is cut through the triangular piece of wood K, 

 as shown by the dotted lines, and then this block is 

 securely fastened to the back of the large board, as shown 

 in the second drawing. An opening of the same diameter, 

 and having the same direction, is also cut through the 

 board, and the movable piece, marked I, is put through 

 this hole, as in the drawing. Finally, we want a wooden 

 washer, 3^ inches (& 7 centimetres) wide, as represented 

 at M. This we slip over the long wooden handle, as 

 shown in the second drawing, and this washer rests on 

 the block K, the top of which is 3^ inches square. This 

 makes all the movable parts of the heliostat, and, when 

 we have put in the mirrors, the instrument is finisiied and 

 ready for use. We must have two mirrors, one 6 inches 

 (15 '2 centimetres) square and one 10 inches (25-4 centi- 

 metres) long and 6 inches (15-2 centimetres) wide. These 

 may be made of common looking-glass : but plate-glass 

 with silvered back is far better, and costs only a little 

 more. 



Any carpenter can make this instrument, and the cost 

 will be about as follows: Wood, 50 cents ; labour, $175 ; 

 glass, ^i ; iron nut, 5 cents ; brackets, 50 cents— total, 

 $3.80. When finished, the instrument should have a coat 

 of shellac-varnish, and, when this is done, the mirrors 

 may be put in place, and fastened on with very heavy 

 bands of rubber. This will enable us to take the glasses 



