The author/speakers tone is Joyful, curious, and also sorrow. In the beginning if the work, we see her describe the grass as glistening and overall describing the atmosphere positively and then she goes in to say "Still must I make this mystery my guest?" Which indicates a little bit of an unknown. She also stated "there is no show of beauty to delight" which aids to the sorrow tone as well as later on she goes into describing the night and waiting for the moonlight. Ending it with "To solve for me, I think, this mystery" adding to the curiosity aspect. I hope this helps in some way, good luck!