1. The Gemara asks about whether one is prohibited from going out of his Techum when he is more than ten Tefachim above the ground.
2. The Gemara attempts to answer this question by citing Eliyahu ha'Navi's seven sermons.
3. The Gemara refutes this proof (#3) by saying that the one giving the sermon was not Eliyahu.
4. Eliyahu will not come to herald the arrival of Mashi'ach on Erev Shabbos or on Erev Yom Tov.
5. Raban Gamliel had an instrument similar to a telescope or binoculars.
A BIT MORE
1. For example, does one transgress the Mitzvah of Techum Shabbos by climbing a tall and thin pole (which is not four Tefachim wide) and then leaving his Techum with the pole as it is carried out?
2. Eliyahu ha'Navi discussed seven different topics on Shabbos morning in Sura before Rav Chisda. He discussed those same topics in the afternoon of that Shabbos before Rabah in Pumbedisa, which is well out of the Techum of Sura. It therefore must be that Eliyahu flew above ten Tefachim from Sura to Pumbedisa, which is why he did not transgress the Mitzvah of Techum Shabbos.
3. In fact, he was Yosef the demon, who did not keep Shabbos.
4. This is because it would disturb everyone's Shabbos and Yom Tov preparations.
5. The Gemara explains that he used it to assist in measuring for numerous Torah laws. For example, he would measure the Techum of Shabbos with it by seeing where 2,000 Amos ended.