HELIOTROPES. 249 



contribute to promote science ; an obelisk in a garden or 

 park might be both an embellishment and an heliotrope. 



Any person that is curious, and enjoys the advantage of a 

 good horizon, might, with little trouble, make two helio- 

 tropes, the one for the winter, the other for the summer 

 solstice ; and these two erections might be constructed with 

 very little expense ; for two pieces of timber frame-work, 

 about ten or twelve feet high, and four feet broad at the 

 base, and close lined with plank, would answer the purpose. 



The erection for the former should, if possible, be placed 

 within sight of some window in the common sitting parlour ; 

 because men, at that dead season of the year, are usually 

 within doors at the close of the day ; while that of the latter 

 might be fixed for any given spot in the garden or outlet, 

 whence the OAvner might contemplate, in a fine summer's 

 evening, the utmost extent that the sun makes to the north- 

 ward at the season of the longest days. Now nothing would 

 be necessary but to place these two objects with so much 

 exactness, that the westerly limb of the sun, at setting, 

 might but just clear the winter heliotrope to the west of it, 

 on the shortest day, and that the whole disc of the sun, at 

 the longest day, might exactly, at setting, also clear the 

 summer heliotrope to the north of it. 



By this simple expedient, it would soon appear that there 

 is no such thing, strictly speaking, as a solstice ; for, from 

 the shortest day, the owner would, every clear evening, see 

 the disc advancing, at its setting, to the westward of the 

 object ; and, from the longest day, observe the sun retiring 

 backwards every evening, at its setting, towards the object 

 westward, till, in a few nights, it would set quite behind it, 

 and so by degrees to the west of it ; for when the sun comes 

 near the summer solstice, the whole disc of it would at first 

 set behind the object : after a time, the northern limb would 

 first appear, and so every night gradually more, till at length 

 the whole diameter woidd set northward of it for about 

 three nights ; but, on the middle night of the three, sensibly 

 more remote than the former or following. When beginning 

 its recess from the summer tropic, it would continue more 

 and more to be hidden every night, till at length it would 

 descend quite behind the object again ; and so nightly moro 

 and more to the westward. 



