Berachos, Chapter 9, Mishnah 2. The Mishnah continues to deal with the various berachos, and here it lists the berachos said over natural phenomena and over the sights of creation.
"Al hazikin ve'al hazeva'os ve'al haberakim ve'al hare'amim ve'al haruchos - omer: Baruch shekocho ugevuraso malei olam" - over comets, over earthquakes, over lightning, over thunder and over winds, one says: Blessed is He whose strength and might fill the world.
"Zikin" - shooting stars.
"Zeva'os" - earthquakes.
"Berakim" and "re'amim" - lightning and thunder.
"Ruchos" - winds, and especially powerful winds.
The meaning of the wording of the berachah: the strength and might of the Holy One, Blessed is He, fill the entire world.
"Al heharim ve'al hageva'os ve'al hayamim ve'al haneharos ve'al hamidbaros - omer: Baruch oseh ma'aseh vereishis" - over mountains, over hills, over seas, over rivers and over deserts, one says: Blessed is He who makes the work of creation.
This berachah is said over anything that has an impressive appearance, and its meaning is: Blessed is Hashem, who created the work of creation.
Over the first group - shooting stars, earthquakes, lightning, thunder and winds - one may also recite "oseh ma'aseh vereishis." But over mountains and hills, seas and rivers, which are fixed things that stand in one place, one must recite specifically "oseh ma'aseh vereishis," and one does not recite over them "shekocho ugevuraso malei olam," since they are visible only in a particular place and at a defined location, unlike the first phenomena, which occur throughout the whole world.
The view of Rabbi Yehudah regarding the Great Sea:
Although we said that over seas one recites "oseh ma'aseh vereishis," Rabbi Yehudah says: "Haro'eh es hayam hagadol omer: Baruch she'asah es hayam hagadol" - one who sees the Great Sea says: Blessed is He who made the Great Sea - a special berachah specifically for it. "The Great Sea" can be understood as the Mediterranean, while according to the Rosh it refers only to an ocean itself, such as the Atlantic or the Pacific.
How often the berachah is recited:
For all of these sights, the berachah is not said every single time. One who travels to high mountains recites the berachah, but he does not recite it again each and every morning; rather, "bizman shero'eh oso lifrakim" - only when he sees it from time to time. The Gemara explains that this means every thirty days. Once thirty days have passed in which he has not seen the place, he recites the berachah again.
With lightning and thunder, however, the law is not so, since these are occasional phenomena that occur from time to time. Therefore, if a new storm came after the skies had cleared in the meantime, one may recite the berachah again.
Over rain and over good news:
The Mishnah continues: "Al hageshamim ve'al besuros tovos" - over rain and over good news. Some hold that when the Mishnah says "rain," it refers only to a case where there was a mild drought and a withholding of rain beforehand, and then one recites the berachah. So too over good news one recites the berachah that the Holy One, Blessed is He, is good and does good for others as well.
And to whom does this berachah apply?
Some hold that it is recited only by someone who has a field and holds it in partnership with another, so that the benefit affects his partner as well.
And some hold that anyone who owns land recites it, even without a partner, because he is truly a partner with all the landowners - the other farmers who suffered from the drought and now have relief.
And if he has no field at all, he recites a different berachah. The Gemara brings a lengthy text: "We thank You for every single drop that You brought down for us," and it continues with the language found in the prayer of Nishmas, until it reaches the concluding words of the berachah. This is a special berachah that was instituted for this.
Over bad news:
The Mishnah concludes: "Al besuros ra'os omer: Baruch dayan ha'emes" - over bad news one says: Blessed is the true Judge - who judges us fairly and justly, and we must accept what He brings upon us with the understanding that it is truly good. Even so, we cannot recite "hatov vehameitiv," because we cannot actually feel the good. The Gemara in Pesachim says that in the future "hatov vehameitiv" will be said over everything, but in the meantime, over bad things we recite "dayan ha'emes."
In summary: In this Mishnah we learned the two basic berachos over the sights of creation - "shekocho ugevuraso malei olam" over fleeting phenomena that occur throughout the world, and "oseh ma'aseh vereishis" over fixed sights that remain in their place; Rabbi Yehudah's special berachah over the Great Sea; the rule of "bizman shero'eh oso lifrakim" - once every thirty days, as opposed to lightning and thunder, which are occasional; and the berachos over rain, over good news and over bad news.